Since there's no real place to get good Prime information (the manual included with the emulator is out of date), here's a thread where you can post things you found. Please try to keep it down to one post per person by editing in new content. Also, feel free to put in something found by someone else, as long as you give attribution.
Prime Emulator Download Link:
http://tiplanet.org/forum/archives_voir.php?id=19496 (adriweb (http://ourl.ca/19209;msg=302932))
It can be ran with no issues in Wine, for those not on Windows.
Function information:
Use the on-calc help. Browse by pressing Tree and using the screen or the arrows, or by pressing Key and pressing the first key you use to get to a function.
Mathematics:
When multiplying a constant by a variable, you have to use *. (2*A+2 instead of 2A+2) (DJ Omnimaga on IRC)
Text diplay:
To color text, you have to use one of the TEXTOUT functions with a RGB function as the color.
If you feed a TEXTOUT function a negative length, the text is italicized and underlined, ignoring the background color (if supplied).