The 70-200mm cost me more than I ever thought I could pay for a lens... honestly, I went and bought it and shot with it for two days but wouldn't tell anyone what it cost me. I was ashamed that I'd spent so much... but the results were so amazing that I didn't really regret it. It's the first lens I've ever purchased, that when I zoom in on my image to 100% on my camera, I can make out all the details. The results are amazing.. and I never really thought the price would be justified.. but it is. I like the idea of buying a lens and knowing that there isn't something that I wanted more and still longed for.
This is going OT... but I agree completely with the 'buy the best glass you can' idea but it's hard to do on the ultra wide end if I want to future proof my lens for owning an FX sesnor later.
My ultra wide right now is the sigma 12-24mm f/4.5-5.6... a slow, huge lens. A 14-24mm f/2.8 would great upgrade to my sigma, but it's a lens I'm not sure I really
want. (A $1500 lens that I can't put a filter on... kinda scary.) On the other hand a lens like the 17-35mm f/2.8 would be a good option for a ultra wide of FX.. but it doesn't help me much I keep my D200. A 17mm isn't wide at all on the cropped sensor.
So my option is to buy DX glass (Tokina 11-16mm f/2.8) at $600 that I'll have to upgrade later or buy the 14-24mm that I'm afraid of.
I'm 90% sure I'm going to try to hock the unopened D700 when it arrives and invest in better glass... and thinking it over now, I think it might make the most sense to pick up a 11-16mm tokina (for the time being) and a used 17-35mm nikon. The latter of which will be my UW when I go FX.