Jelly Bean for OG i9000
For real, you ask? Alright, hit the break and I'll tell you the rest.
Two XDA-Developer members, DerTeufel1980 and be18 managed to port and compile the latest version of Android, 4.1 Jelly Bean to the phone which pioneered Samsung's kingship in Android manufacturers. They say it's running pretty smooth, unlike the ICS which has been buggy when run on the phone, until now.
It's all working good, although there are sure to be some issues. Major issues noted by the developers are Google Now bugs (the fix was uploaded, hit the source at the bottom) and the inability to mount your external SD to your PC. The second one is a deal breaker to me, since I'm going to hand this phone over to my sister in a few months (and hopefully saves up enough cash to bring a new phone home). Additionally, some people (not all) also have some issues about sound, keyboards, etc. which are minor issues; very common among new ROMs. What's impressive is that people report only few to no lags at all when running this ROM.
If the issues above doesn't stop you to get the taste of Jelly Bean, or you're a very brave man, you can hit the source below for download guide and instructions. I won't be able to answer your questions, since I don't flash this ROM. This phone I'm holding is still working good, and better still be until I hand it over.
Source (Download + Instruction)