Good luck. At the worst you should be able to reflash the stock kernel and stock system via odin and get it back. If you can get to the Verizon logo, it's not that bad.
If flashing the clockwork kernel/ recovery kernel doesn't work, try the stock kernel and stock /system here.
It's not that complicated, the problem is that it can seem that way if you don't know how it was applied in the first place. This is why I advocate against most one-click solutions.. Many don't come with an "un-click", and you can't see what's going on behind the scenes.
Always try and do it by hand, from the shell. Then you know what exactly was changed, and someone can easily help you reverse it.
That being said, what the lag fix does is create a 'virtual' partition with a more efficient file system. It then copies your /data to the virtual partition. Then it removes that /data, and creates symbolic links pointing to the new virtual partition. That makes it compatible with most every app that gets installed to /data.
If you can't find another thread/post with someone describing how they undid it, I would jump on IRC when you have time and see if someone in #samsung-fascinate or #android-root will help you out.
I used the one click lag fix. I will spend some time later trying to figure out how to remove it manually. Worse case I will use the revert to stock with Odin idea, then re root and do another Nandroid backup.
I did the same thing with the factory reset but it still leaves the debing fix with the filename with the .old extension
I prefer that as long as the lag fix has been removed or do I still have to recover using the odin back to stock >