My issue with the search is that it tends to bring back a lot of irrelevant results, I think mainly because it searches as "OR" all the time. If I search for a thread that I know exists that was, say someone spilling beer over their MacBook and search for "beer" and "MacBook", I get a lot of threads that are about beer, and a lot of threads about MacBooks, but it's hard to then pick out the ones that are about beer and MacBooks.
I find I have to try and remember another random word that was said in that thread and search for that too, or something I know a certain poster said. It's all very well if you know a thread's out there, but not so useful if you're someone new on the site looking for information who just isn't going to get relevant results.
It's ok if you're searching for one word, but I don't find it very useful for anything more. Being able to search in quotes for a particular phrase would be helpful (and would help the above problem to an extent) but being able to search for "AND" as well as "OR" would be much better. I seem to remember getting better results with the old search, which I think was "AND"; although there were fewer results, they were a lot more relevant.