I have a unibody MBP (removeable battery)-- 2.53ghz, 4 gig ram. I get the rainbow wheel on a regular basis. Yesterday I had iTunes and safari open. iTunes was downloading some new podcasts and I was browsing the app store. It froze a couple times when navigating around iTunes and gave me the rainbow wheel. Another point while it was downloading and I was trying to delete some music and it did the same thing a few times. My Powerbook with 2 gigs ram never froze/lagged as much as this one does. Anyone else experience this?