We have good news and bad news (x2), world. The good: the first CM6.1 build for the Samsung Galaxy S has been released. The first (and worst) bit of bad news: at this point, it looks like it's for the GT-i9000 only, and not the US versions of the SGS (though I'm no dev, so I'm not positive). The other bad news: this is apparently a very bug-laden release ("Holy crap, it's full of BUGS!").

Developers codeworkx and coolya have been working on this for quite some time, while keeping the very impatient SGS owners regularly updated on their progress via the CM forums. Today marked the first release of the build, to which they've attached a beta stamp.

Performance has received a huge bump; these numbers aren't record-breaking, but they're a major step-up from stock:

Quadrant CyanogenMod / data/dbdata on EXT4: 2369
CPU: 5152
Memory: 1773
I/O: 3685
2D: 310
3D: 923

Quadrant JPO / complete on RFS: 952
CPU: 1326
Memory: 1622
I/O: 625
2D: 295
3D: 590

Even running the beta build, switching the filesystem from RFS to EXT4 provided a Quadrant boost of nearly 750 - not bad.

CM6.1_i9000_quad1 CM6.1_i9000_quad2

Left - RFS; Right - EXT4

Installation isn't especially complex, but it does have some specific requirements - not surprising, given just how early of a build this is. In fact, I don't mean to harp on that point, but this is one of those times it's really necessary: this is a very early build. You can very easily brick your device here, and if you don't follow every step to the letter, you'll do just that. If you have even the slightest doubts, I'd suggest waiting a short while for a more solid build.

Installation instructions:

- First time flashing CM 6 to your GT-I9000?
1. Make sure your phone is fully charged! Update process will take some time.
2. Make sure that you've not applied any lagfix to your phone. Otherwise remove it!
3. Make sure you're actually on JPM Firmware or newer. If not, flash and boot into it. We need this Modem Firmware!
4. Download initial Kernel (link below).
5. Download CyanogenMod (link below) and copy it onto your internal sdcard. Don't extract!
6. Optional: Download Google Addon (link below) and copy it onto your internal sdcard.
7. Make sure you have more than 500 MB free space on internal sdcard.
8. Flash initial kernel "cm_kernel_initial_GT-I9000.tar" as PDA via odin (no pit, no repartition).
9. Reboot into Recovery
10. Do a Nandroid Backup. Choose "Backup and Restore", then "Backup". It's very important!
11. Go back and do a factory reset / data wipe. It's really necessary otherwise your phone won't boot.
12. Choose "install zip from sdcard" -> "choose zip from sdcard", choose CyanogenMod and apply it! This will take some time!
13. After this your phone should boot. Don't touch it for a few minutes, it has a lot to do.
14. OPTIONAL: Enable Wifi, reboot to recovery and flash Google Addon (choose "install zip from sdcard" -> "choose zip from sdcard" -> "gappsXXX"). Reboot!
15. Setting up your google account can take some minutes. After this you should enable Wifi immediately!
16. Do not use GPS. It'll kill your phone.

- Upgrading from earlier CM6?
1. Do a Nandroid Backup!
2. Install the ROM (your Google apps will be backed up automatically)

Based on user comments in the threads, this definitely is a tricky process, and the build is still fairly hectic. Still think you can handle it? Head on over to the CM forums link below for details and to download, or hit up either of the related XDA-Devs threads for more info.

[Souce: CyanogenMod Forums, XDA-Developers (1) (2)]