My European colleague and I (in US) can't be the only two ID users who need some kind of online version control for our ID docs! We'd be interested in reading what others are doing to solve the problem of sharing documents online, tracking changes, etc... all the features you'd expect from a desktop based version control tool, only online.
You can do something similar via dropbox. I regularly use this for my clients in the UK and US. Basically it's just a folder that you can both copy files into and they will appear on each others desktop. Ideally, you would then copy to your desktop to work from and save back into Dropbox for the next round.
Also, for review purposes, you could use Adobes CS Review tool in Acrobat.com which can be accessed straight from InDesign. It's free until April this year (apparently).
Edit:// I meant to add, you can track the changes via story editor. Haven't tested this with any image/layout changes though.