What I did with my 2.2 i7 15":
BTO 128GB SSD in main location, on this I have all my apps and essential to the system items (logic files, or any other program files)
Optibay 750gb 7200rpm drive:
Logic song projects, iTunes library, Downloads (went into every app and manually selected this one, though you could make an alias)
Then all my normal documents (work etc) are also on the 750gb but with aliases that link to it on the desktop so i don't have to go to the 2nd drive any time I want something. This works really well and I still have 77gb available on the SSD