>I was hoping to ride the twitter tersity trend :-)

Mc_Big_G's advice notwithstanding (actually, my initial reaction is to agree with him...let's see if that feeling lasts-- as I grab at my own gaseous thoughts and force them to solidify so I can stack them atop one another and build-- over the course of this post), if you were to make an attempt at said trend after all...

Why not do 140 characters?

My guess is you went with 150 either to be different from Twitter or just because it's a nice, round number. Neither mode of thought is worth condemning. Makes enough sense.

But consider the following:
140 is the same character limit as Twitter. "Duh, he already knew that. That's why he chose 150: to NOT be the same as Twitter." Whoa, you're right, you're right, but hold on there, cowboy. If you were to have the exact same character limit as Twitter, you could let users post items, respond to posts, and communicate with other users via Twitter!

How HUGE would that be? You know what the 100-foot-tall hurdle for EVERY Craigslist competitor ever is? The chicken-and-egg problem. Hell, as soon as I clicked your site and searched my area for "rent", I knew (well, thought) 'chicken-and-egg' talk was, by itself, going to be the only content of my feedback post.

The users won't come if you don't have any postings, but you won't have many postings unless you only have a few users. Growth is usually very difficult to achieve in these scenarios. But if you utilize Twitter to the best of your ability, it's like hijacking a chicken farm truck on its way to the supermarket. The truck, incidentally, will either look like it's carrying a lifetime supply of Easter decorations, sans paint and frustration, or like a German POW-transport vehicle circa 1940 (zing, Frenchies!)(just kidding, I love French people)(I hear they make great toast). Depends on which (eggs vs. chickens) are users and which are item postings in our analogy. The point is you get a ton of users on the cheap.

Where to go beyond there:

a) Make all forms of typed communication (person-to-person convo, item posts, et al.) possible via Twitter. For example, get some tweetbots to relay posts for that user's desired geographical area(s) and/or desired categories ("I need a used TV really bad! I know, I'll 'follow' the TownFlierElectronics(1) tweetbot!" Bam. Free targeted ads, increased user return rate, superlow barrier for users to relay info about your site/communicate with their followers about you, i.e. word-of-mouth advertising, the Holy Grail). BUT...

b) Leave what else you can on your site (pictures of items, contact info, maps, et al.) and be sure people know those things are available over there, just one click away. Consider automatically inserting [PIC] on the end of item-post-tweets, for example. Massive jump in traffic if you exploit that to the best of your ability. And a massive jump in traffic means a massive jump in revenue, amirite? ;)

(1) Obviously, implicit here is yet another recommendation; namely, go register a Twitter account for every TownFlier[city/area name], every TownFlier[category], and every TownFlier[popular/common keyword] you can think of. Throw in some others too, of course: TownFlier[news or blog/special deals or freebies/whatever you want].

I'll leave it to you to figure out how you want to accept item post/reply/etc. information (i.e., anything you are or could cap under 140 characters) from the user's Twitter account through your tweetbots to your site. Surely, there are plenty of options-- so many that whatever I might've recommended would likely not have been the optimal solution by sheer statistical probability.

c) Hardest to accomplish, and high risk/very high reward: Brand yourself as Twitter's Craigslist. Unless that already exists. I have no idea. A pun (even a visual one, like just the logo) involving tweeting/Twitter/birds in general and TownFlier can't be that hard to come up with. Maybe work in '140' somehow, if you can.

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Hope this helps, and good luck with your startup.

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(Fuck, I love talking product and market strategy. Too bad I can't hack for shit...yet.)