Good thread Jonny, as Im in the same boat.
I think the HD Cams for web use, is overkill, as you will never really benefit from the amazing quality.
For professional film making though, I think go for it. As soon as I have the dosh, the Sony HVR A1E will be mine (and judging from the £1700 you quoted, you're thinking the same as me)
its an expensive gamble, and depends on what you plan to do, but I think eventually, it will be worth it.