The first post will be updated as more and more people reply with some good tips and tricks that you may not know.
to take a screenshot:hold the home button (that square button on the bottom of your phone) and press the top right power button. the screen will flash white, your screenshot is now in your camera photos, you can email or mms it.
To disable I-tunes opening up every time you connect your Iphone - press Ctrl-Alt-Delete and under processes close down "Ituneshelper". I would also delete the opening of this process from the registry. If you want a very easy way to see which programs open automatically in your registry, clean out temporary files and other crap, and fix registry errors, this program is amazingly awesome and 100% freeware.
http://www.ccleaner.com/
To record video on your 2G/3G - so yeah... Iphones not named 3GS can't even record video, (weaksauce).
But there are ways to do it. currently the best program (that I know of) is called Cycorder, It is free (yay!). Just open Cydia and search for "Cycorder" and install, you're good to go. Here's the FAQ on it.
http://cydia.saurik.com/info/cycorder/questions.html
You will have to SSH (see
http://forum.ppcgeeks.com/showthread.php?t=112607) to get the video to your computer for now. The FAQ shows you where the file is stored.