Rainbow wheel when typing fast

I am using a Mac Mini, (wireless apple keyboard and track pad) and about 2 months ago, when I type fast, especially in Mail, but also in Safari, and Pages I get the rainbow wheel, and have to wait for the computer to catch up with my words. The whole thing seems slow, and the rainbow comes on with the finder as well. Any editing, moving the cursor to a different place, or backspacing tends to make the rainbow wheel. I repaired disc permissions, in safe mode. I reset the whatever its called on startup...and now I would like to just bring it in to a retail store...