According to a few links I've looked at it's under the hood changes (bug fixes and optimizations) only for the ogS but adds new features to the S2.
Since I'd figured the S1 was abandoned by Samsung and it's working fine I'll be patient waiting on AT&T to push it to mine. XDA had 1 user complaining of lesser battery life when remotely connected but others chimed in stating they didn't have the same problem. If you do have performance issues after the update try a factory reset, just like the remedy for phones and tablets after firmware updates to enhance performance.