I recently went from a 450d to a 1D Mk2 just as you did, it was a good move, the 1D is weather sealed which was one of the main attractions (at Rally GB water was pouring off it and it never missed a beat) and the AF is a massive improvement over the 450d.
I too use a 70-200 F4 IS and a 50mm 1.8, I bought a 24-105 F4 IS for a walkabout lens and have been pleased with that.
The menu system takes a bit of getting used to but when you do it is good and quick.
The only thing I wasn't too sure about at first was the much smaller LCD screen but after a few weeks I've found that it is no major problem really. Similarly I only ever used live view on the 450d when on a tripod, I just have to go back to the old fashioned viewfinder but it is no issue.
Batteries are much heavier for the 1D, I had three batteries for my 450d and thought I would need similar for the 1D2, I shot 900 frames over 2 days at Rally GB on one battery with it switched on all the time, AF and IS running and was still on full battery when I went home, they are bulky but impressive. I wish battery chargers were a little cheaper so I could have one at work but again with the charge they hold it isn't a problem.
Finally the 1D2 is a lot bigger, bulkier and heavier but in use it doesn't feel it, particularly with a bigger lens on (the nifty fifty does feel comical hung off the front!), you do notice the weight when carrying it in a bag though, I've just bought a big Tamrac Cyberpack 8 for all my gear to spread the weight across both shoulders, at one point in the mountains of wales the weight of my old Stealth Reporter hanging asymetrically across me overbalanced me as I descended through a wood and I ended up on my arse!
To conclude (sorry for rambling) you'll not be disappointed.
