Interesting. If it helps the server is running the lastest PHP version (currently 5.2.0, 5.1.6 before) as FastCGI under LightTPD

The directory is still filling up with sessions:

Code
bouncer:/var/webs/philipp# cd sessions
bouncer:/var/webs/philipp/sessions# find . | wc -l
3605
bouncer:/var/webs/philipp/sessions#

frown