The following features which can usually be found in ROMs running on SGS hardware are not currently available using CyanogenMod 7 on the i9000:
Lets get this out of the way first.
Most users no longer feel battery life is a significant issue.
However in the end, it is VERY individual so all you can do is see for yourself.
Totally unsupported
High resolution video tends to stutter.
The workaround is to use a lower resolution while filming or decrease the framerate.
(some users have installed lgCamera, which allows you to change bitrate and codec easily)
- Video Call via Dialer
Not part of the ROM at this time and won't be in the future, unless Google adds it to the framework (Samsung hacked this into Android's framework)!
- Hardware accelerated video playback
Just like Video Calling above, this was hacked in by Samsung and is not part of AOSP. If your system player has problems with HD videos, use MoboPlayer (which uses soft decoding) and/or DicePlayer (which uses hardware acceleration, but isn't free) as workaround.
- Call Recording
Call Recording was discussed multiple times and the devs decided not to implement it in CM7 as it is illegal in many countries.