I played with the new iMac today in the Apple store just to check it out first hand.
I must say it is noticeably faster. iLife just screamed.
I am not in the market for a new desktop right now, but I will upgrade my wife's mac mini with either the new mini or an iMac this year. I hope the mini is a big update since my wife wants to keep her 23" display and prefers that over the iMac.
Personally speaking, the iMac experience makes me look forward to the new PowerBooks. Here I think the speed difference will be most noticeable given the FSB issues with the PowerBooks.
I am planning on upgrading the PowerBook in early 2007, but I highly doubt I will last that long. I predict that I will buy the MacBook Pro when it comes with a 17" screen. (Assuming there aren't reports of issues with it.)
Either way, I think the move to Intel is going to be great.