Format Only Edited Lines
The "Save Actions" is one of my favorite features in Eclipse 3.3 (read my original post about it). In Eclipse 3.4 there are several improvements including some new formatting features. One of the complaints against the Save Actions feature was that it will change the entire file, thus, making it very hard to compare to previous revisions when using a source control. It can become very annoying if some team members use it and some don't.
For that purpose there's a new feature which allows changing just the edited lines, keeping the rest of the file intact. I highly recommend using the Save Actions feature. It is inactive by default, so go ahead and activate it.