Subversion has a superb client on Windows (Tortoise, of course). Everything I've tried on Linux just - well - sucks in comparison....
Answer
Disclaimer: A long long time ago I was one of the developers for RabbitVCS (previously known as NautilusSvn).
If you use Nautilus then you might be interested in RabbitVCS (mentioned earlier by Trevor Bramble). It's an unadulterated clone of TortoiseSVN for Nautilus written in Python. While there's still a lot of improvement to be made (especially in the area of performance) some people seem to be quite satisfied with it.
The name is quite fitting for the project, because the story it refers to quite accurately depicts the development pace (meaning long naps). If you do choose to start using RabbitVCS as your version control client, you're probably going to have to get your hands dirty.