I'm not a gurus la but it should be ok. I just installed on mine with ODIN.

This is what I did.
1. Upgrade my sgs maxis to froyo via KIES a couple of days ago
2. Rooted with z4root from market
3. Apply the 3-button universal fix with ODIN3 (make sure that you enabled USB Debug)

This complete the stock JPA with root and 3 button fix. Next for the YA-OK.
1. Download YA-OK 1.3 and extract .tar to a folder
2. Next restart SGS with Home+Vol Down+Power to get into download mode
3. Fire up ODIN and select JPA with the extracted tar file
4. Unticked re-partition, ticked auto reboot
5. Connect to PC (make sure your SGS now in Download Mode)
6. Then click start with ODIN and waa la - you using YA-OK without lagfix
7. To enable lagfix, reboot your SGS again with Home+Vol UP+Power until your see the screen start displaying all kinds of YA-OK option
8. Select whichever option you want for the lagfix, for me, now using Voodoo ext4 as my lagfix (backup and restore option)
9. Once you have selected that, keep selecting back until you get to the main menu, and select system reboot.
10. During the reboot, it will start doing the lagfix, backup and restore. Probably take about 5 minutes.
11. Done - YA-OK with Voodoo

Just ran some simple test. I've installed YA-OK 1.3 and I'm not sure what is the problem of lagfix that's everyone said cannot work with this DXJPA. For me the lagfix is working nicely and I can enable and disable them. SpeedMOD K8 is now also available which is supposed to remove this issue.

Anyway, after the installation, Quadrant Standard showed a result of 1000 with this mod without lagfix or overclock, s0 a score of 1000 which is slighly faster than the stock JPA or 900.
Next enable lagfix, and the score went up to 1750 (both voodoo and ext4 for all).
Next disable all lagfixes and apparently it works as well. Now I'm running without lagfixes and its like running a P3 CPU over Quadcores.

With lagfix ext4 for all filesystem



Without lagfix (this is disable to standard filesystem after running the above)



However, there is a problem with battery draining. When the lagfix is enable, the Back and Menu button lights is on during idle or lock mode. Not sure what is causing this, will get more info in XDA forum for this issues.

My main concern is still the battery usage which is not that easy to test, will leave the phone idle tonite and see how much usage with ext4 lagfix.