I'm seeing a fair number of hacker/fitness articles at HN, and there are some long-live well-known instances online (John Walker's "Hacker Diet", Jeremy Zawodny "Diet Tips"). At the same time, there's a lot of naiveté in many of the comments.

A few basic principles might be helpful here.

1: It's really not that complicated. There are a few well-known principles of weight/fat gain and loss, cardiovascular fitness, and strength / hypertrophy (muscle building) training. You'll get a long way with sound nutrition based on good food choices, appropriate caloric intake for your goals, and the right mix of both cardio and strength training modalities (methods). A decent starting point is Liam Rosen's "Beginners Guide": http://www.liamrosen.com/fitness.html Understand concepts such as SAID / training specificity, progressive overload, and caloric balance.

2: Do some research. The Wikipedia "Strength Training" article covers basics of sets, reps, weights, and rest periods for use in strength training. ExRx.net (http://exrx.net) has a lot of solid information and exercise guides. YouTube is a great resource for finding form videos (both good and bad) for exercises. Watching Olympic lifters is inspiring, watching "fail" vids has its own benefits.... Read Michael Pollan, Andrew Weil, and others on diet. I'm not a nutrition nazi -- there are a huge range of native diets, people vary, and lifestyle demands vary, though I'd suggest minimizing the highly processed crap you eat (and a lot of foods you might not consider "highly processed" or "crap" are). But go ahead and read Dean Ornish (low-fat), Atkins (low carb), Vegan (no animal products) classic old-school bodybuilding (BIG FOOD, high protein) sources. Figure out which seems most sensible and appropriate to you. Jack LaLanne got a ton of stuff right in the 1950s. Understand your basic macronutrients (carbs, protein, fats) and how they're used by your body.

3: Read a good book on fitness. One of the best I've seen in the past decade is The New Rules of Lifting by Lou Schuler and Alwyn Cosgrove. It covers basics of fitness, nutrition, strength training, identifies six foundational exercises (squats, deads, lunges, "push" (presses), "pull" (rows/chins), and twist). Coverage of some of the more technical lifts (squats and deads) is limited, I'd suggest Mark Rippetoe's comprehensive and excellent Starting Strength, for this. I'm a fan too of a good 5x5 program (such as Rippetoe's or as you'll find at http://www.stronglifts.com/). "New Rules" includes a suite of training programs aimed at various goals, which others may like. Body for Life is another good pick. There's considerable scholarly research on strength training as well, Google Scholar is a good place to do some digging (but don't obsess with minutia and details).

4: Realize that this is a long-term, lifetime project. Start light, start short, start easy. But start. Increase the intensity and duration of exercise gradually over time. Too many novices obsess over how much weight they should use, what intensity they should exercise at, or how long they should move. It doesn't matter, and lighter/less is better initially. The 5x5 programs above start light and add 5# per lift per workout (10# for deads). Believe it or not, this is a rapid progression, and though the programs start very easy, they get challenging within a month or two. You'll stick with them for 3-9 months typically, then switch programs according to your goals.

5: Training should be balanced. This doesn't mean doing everything every day. It does mean that you want to include both strength and cardio, that nutrition and exercise matter. That you want to train your front and your back (no, pushups and crunches are not a comprehensive training program, and can lead to or exacerbate imbalances in the long run), your top and your bottom, multiple planes of motion (sagittal tends to dominate, transverse and frontal are neglected), varying rep/set/weight ranges (strength: 1-6, size: 8-12, endurance: 15+), both interval and long-duration cardio. Compound/whole-body and freeweight lifts are generally preferred, though isolation movements have their place, especially in bringing up weak points or for rehab. Bilateral (balanced) and unilateral (one-side at a time) movements. Excesses in any one dimension can be bad (look up the bone-loss issues of competitive cyclists for some really interesting reading).

6: Rest and recovery matter. Training is stimulus. Food is fuel. Recovery is when your body adapts to stimulus with what you feed it. Yes, you really can burn fat while you sleep (and do routinely).

7: Intensity matters. If there's one error I see at gyms, it's working out at too little intensity, usually cardio, for too long. I can point you at a 4-minute workout that will 1) have you trying to get your lungs back inside you and 2) have very significant impacts on your cardio potential as measured by VO2 Max (it's called Tabata intervals, Google it). Yes, this is what that idiotic $14,000 SkyMall exercise thing is based on, but you can do 'em with minimal equipment -- jumprope or burpees -- among other alternatives.

8: Training should be goal-oriented. Define your goals (usually something like "lose fat", "gain muscle", "run faster", "get over this nagging <insert problem here> issue". Find out what training modalities work best for this. If you're working with a trainer ask WHY you're doing a particular exercise or training method.

9: You're not that special. Premature optimization of fitness regimes is the heart of much fitness evil. Start with a basic program. Especially as a novice, you'll make rapid gains -- and as a consequence, you'll think you've found the One True Way. That's complete bullshit -- you've just experienced the Novice Effect (Google that). As you progress toward goals, training specificity will increase -- you're tailoring your program to both your goals and your body's ability to adapt. You'll learn about training cycles (sets/reps, weekly, meso, and macro cycles).

10: There's a ton of fitness information on the InterWebs. Some of it's silly/stupid/biased, some isn't. I've noted a few good starting points. T-Nation (mentioned by others) has an active forums section, as do other fitness sites. Share knowledge. It's not just for IT/CS problems.

Answering the original post: I'd say techies (or anyone) would benefit from a weekly exercise regime consisting of 2-4 days of whole-body freeweight training, a HIIT cardio session or two, and an endurance cardio session or two. Addressing typical issues such as upper-cross syndrome, weak posterior chain, excess carb consumption, and generally neglected muscular strength, particularly lower-body (legs, glutes, spinal erectors) will matter. How far you take this is up to you, but you'll be stronger, hurt less, do more, and as you get older (it will happen, eventually), look and feel better. Especially naked.