Just a quick note on the hotfix that was released quite a while ago to improve compile times on R2. Many blogs including the official Microsoft one linked directly to the hotfix, and many people have installed it immediately with no result. What many people don't seem to know (and honestly in my own haste to try it out I did the same thing at first) is that you need to update your model store schema to benefit from the improvements which included new indexes in the model store.
So, if you have installed the hotfix (KB2844240), make sure to run "axutil schema" on the model store to actually make the changes take effect!
Source Joris dG