I have been using IntelliJ 13 for the last month (as does my whole team). I am using a Mac 2.3GHz i7, and 16GB, 64bit.
java version "1.7.0_40"
Java(TM) SE Runtime Environment (build 1.7.0_40-b43)
Java HotSpot(TM) 64-Bit Server VM (build 24.0-b56, mixed mode)
When ever i do a refactor->move, or rename it can take as long as 1 min (single class) or > 1hr for a group of clases. CPU hits 110%
Intially IntelliJ was only using up to 510MB, which was suspisciously close to 512 so i increasedt he max memory to 2GB, right now it sits around 1GB, so I know that change worked.
That had no effect on the speed, so then per a SO post I deleted the ~/Library/Caches/IntelliJIdea13 folder and let intelliJ rebuild the cache/index, and it worked for that session. Also if a re-clone my git project into a new folder and open with intellij, it works faster.
Other than this problem I love intelliJ. Not sure if it is relevant but I also paid for the license recently.