The lag is created by the flawed file system in the Galaxy. I can confirm that Froyo does not fix the lag, there might be improvements but the overall effect is minimal.
This is noticeable if you use your phone moderately-heavy, using many apps and email etc.
The only thing that has actually fixed it for me is:
1. Root (used z4root) @Market
2. Installing OCLF (one click lag fix)
[APP] One Click Lag Fix APK - 2.0 - xda-developers
Whole different phone. But read up before doing this, do it wrong and you can brick the phone and you will have to re-flash etc. Rooting the phone voids warranty but can be reversed - but again make sure you read all the instructions.