[EVO 4G Q&A, Help & Troubleshooting] thecodemonk:
I see most of the questions have been answered above...I'll attempt as well and perhaps it will help clarify (or just give a different way of looking at it).

Yes, the kernel is the heart of any OS (Windows has one, Linux has one, etc). The kernel is where everything eventually goes to do anything.

The reason the new kernels do not have camera functionality is because, while we have generic source code, we do not have the drivers/modules for that source code. HTC does some modifications within the source that are proprietary and so we have to attempt to try and reverse engineer it. About the time we do, they release the source code (I have suspicions of conspiracy, but that may just be me) and that's when the kernel's really roll out with some fun stuff. :)

New kernels will be the source of the most new features...overclocking, efficiency improvements, etc.

This is one of the areas I'm most weak in for understanding but I'll still take a stab.

NAND is a type of flash and, to my knowledge, it's own seperate chip. It is usually locked to prevent modifications that could break your phone or prevent it from updating properly...I *think* it's used during boot so the lock would translate straight through to your OS and prevent changes if put in a locked state (think similar to how some SD cards have a "lock" switch on the side to make it read only, except a software version of it).

Clockwork and AmonRA's recoveries are replacements that add functionality over the stock recovery. The stock recovery is only meant to be used by the manufacturer to perform certain tasks (like updating, resetting, etc...but no user functions like backup/restores.). Both Clockwork and AmonRA's recoveries add the ability to take a complete image of your phone (so that you can always restore any software changes no matter how severe), reformat and partition your sd card (to add/remote a cache partition or a partition for Apps2SD), reset battery stats, and a host of other things I'm sure I haven't even touched on. Also, I believe they add the functionality to flash unsigned updates done by the community (not just restricting us to HTC's updates).

Most of the ROMs you see now require NAND unlocks so that they can mess with the apps in /system. Some ROMs are just a certain package of apps or a set of themes. Others add functionality or make certain things easier to implement. Yet others are tweaked to attempt to change other aspects of the OS to improve performance of battery life through tweaks to when the system performs certain tasks.

Ultimately, each ROM is different and the changelogs *should* tell you what all they've done over the stock (or if they're based on another ROM, you can open that page to see the tweaks they are tweaking, etc). :) (Sometimes it can get pretty big on the tweaks on another rom's tweaks on another rom's tweaks...check the CDMA hero forums for some combination roms :P).

ROMs vs Dev-ROMs - Dev-ROM's are usually a work in progress...they are testing new features and often will be on the bleeding edge (emphasis on bleeding). These will sometimes (even likely) break something while they try and improve or add new functionality in another aspect. You should only flash these if you want to help test and if you have an idea of what's going on so you can help troubleshoot.

Normal ROMs are usually more stable (usually) and will have milder modifications (though once a DEV-ROM has successfully gotten a new feature stable, most other ROMs will incorporate those changes...it's kindof a lifecycle).

Radio images are a bit more like firmware updates to the radio chip. These often help to improve reception or connectivity or fix instabilities or other problems. Not everyone experiences the issues that it attempts to fix and doing a flash on your own does have certain risks. The odds of a problem arising for you isn't high, but the effect is potentially severe if a problem does occur. The main thing to remember is to ensure you have enough battery for the changes to occur (firmware updates in general recommend this on all devices, be it laptop BIOS updates or phone radio updates...I recommend using the wall charger and not unplugging it until 5 minutes after the update has completed), and ensure that you don't try and do anything else on the phone while the update is occuring.

Hopefully the info given by me and my fellow ex-newbies will help with your desire to learn! :) There's a lot of cool stuff about our phones and I love that we can get a bit into the guts of the thing (unlike some phones*)

*I can't help but throw a little jab at Apple every so often. :P