My project is currently using a svn repository which gains several hundred new revisions per day. The repository resides on a Win2k3-server and is served through Apache/mod_
Subversion only stores the delta (differences), between 2 revisions, so this helps saving a LOT of space, specially if you only commit code (text) and no binaries (images and docs).
Additionally I´ve seen a lot of very big projects using svn and never complained about performance.
Maybe you are worried about checkout times? then I guess this would really be a networking problem.
Oh, and I´ve worked on CVS repositories with 2Gb+ of stuff (code, imgs, docs) and never had an performance problem. Since svn is a great improvement on cvs I don´t think you should worry about.
Hope it helps easy your mind a little ;)