I've seen it written many times in the past and in interviews. I really have no way of looking any of that up for you. It's just a thing I've heard many times from many sources.
I can, however, point you to this answer from Apple during the confrence call a few days ago:
Q: Will research and development costs rise due to expected 2010 product introductions?
A: Don't want to say too much. We've been investing in our future right along and have managed operating costs very well. We're being careful with money, making good choices, but continuing to invest confidently.
That sounds mild, but remember how these things work. If Apple says "a little" it usually means "a lot" because they try to play up bad news and keep a lid on good news so that they can beat expectations next quarter. It's just the way they've always worked.
By saying they are investing "confidently" I take to mean "you'd be shocked if you knew how much of our cash we're spending!"