Consider that the 20D apparently is still available new from Beach Camera for $900. Before they were discontinued, I recall they sold for between $1,500 at intro, eventually to $1,200 by the time the 30D debuted.
The 30D originally sold for $1,450, can now be bought for about $1,050 after rebate ($100 unless you're buying something else to get double rebate). Will the 30D be available new for $950 or less when the 40D debuts? It's quite possible, but don't you want to take pictures now?
I bought the 5D and 24-105L for $3,800 almost a year ago, before the current double rebate of $600 off, or $3k for the set. It'll probably sell for even less in another year. Do I have regrets? No, because I was able to take my new camera-lens combo to document a once-in-a-lifetime family vacation. But that's just me.