My current pattern is to merge topic branches into my main development branch once they're finished. The log has been getting kind of crazy to look at lately, and I was considering switching to using rebase instead.
What are the possible disadvantages to using rebase instead of merge for topic/feature branches?
The main disadvantage with using rebase is that you should (read must) only use rebase locally. That is to say, once something has been pushed DON'T rebase it after that. Rewriting history is fine and dandy, but the instant you start screwing around with the history on a remote, things get really messy.
EDIT
Another disadvantage is the fact that the true history is in fact lost. This means, among other things, that it's impossible to go back to the topic branch (easily) since it would have the appearance of being a part of the main branch. It also makes reverting changes much more painful, because you have to cherry-pick one commit at a time, trying your best to remember which ones came from the original topic branch. If you use an interactive rebase, or worse -- squashed your commits down -- then this could be an enormous headache.