My take.. CM7 is not good. It's great!! MISSING some small things like office app, video calling, smooth 720p video recording, low battery drain, fully working FM radio and TV Out etc. If you need these, best not to consider CM7.

CM7 is really suitable for those who want to take their SGS to the next level of Android sweetness, so to speak, but you must have time and motivation to read lots of tutorials, FAQs, and forum postings before u think about giving CM7 a try.

Note : I follow the CM7 thread @ xda-dev religiously, and noobs posting dumb questions there get royally fcuked on a daily basis. I see a lot of stupid questions here i.e. people who either have reading/comprehension problems or have not even read the info compiled in the first few posting of this thread, I can't even imagine what would happen if these were posted @ xda-dev. Credit must be given to the very tolerant and patient sifus in LYN.. 

i just flashed #15 this morning and then #18 was released.
For CM7:
simply galaxy 2.6 is froyo right? if you have never flashed to any gb rom, then you still have froyo bootloader.
- preferably flash ezbase 2.0 first
- if you don't want, clear cache and dalvik cache
- flash latest #18 nightly from CWM and reboot
- flash gapps
- done. enjoy!
- i nvr done nandroid backup. if i screw up, ezbase is there.

for stock gingerbread:
- follow the link that has been posted here to ramad's post.

"The fix has been working on JVK and JVB ROMs, check other threads about this issue. You can delete the data of the Software Update application, but it will be regenerated after a reboot. If you want to get rid of this, just root the phone and delete the following APKs

syncmldm.apk
syncmlds.apk
wssyncmlnps.apk