I bought this a year ago February knowing that the 5DMkII was coming soon, but at the same time I knew the MkII was going to be waaaayyy out of my budget. I couldn't be happier. Got it in time for several trips this past year. This is my first DSLR coming from the EOS ELAN/100 film and Canon A95. Recently pushed the ISO to 3200 for hand held night photography while out about with friends in Bangkok - came out really well, better than I and my Nikon friend expected.
This may be 3 yr old technology, but if you're looking for full frame at a reasonable price, especially now if you can find mint 2nd hand one, go for it. It is worth it. I waited 3 years for the price to drop. On the price/value proposition, I agree with everyone earlier, this is now a really excellent deal if you don't need/want all the bells/whistles of the MkII or if price is an issue.
It is solid feel in hand. My Dad bought the 400D (Rebel)...I did not like the feel of that at all, but he wanted light weight. Yes, the 5D is weighty especially after a full day of walking with my 28-70L (weighty lens itself being an older lens) and a rented 70-200L f/4 on a recent trip.
I'm having a ball pairing the 5D with my 100mm macro, shooting away at flowers, leaves and bugs. :-)