Could be the cache filling up. Try clearing it.
I've had issues with Chromium, where it's been using up all my ram(8gb). I haven't bothered tracking the problem down because it's a secondary browser for me. I /think/ it might be Flash related, but don't know for sure.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.