This is actually a bug in Mac OS X, all Cisco IPSec connections have a timeout (hard limit of the lifetime) of 3600 second (60 minutes) because of the soft and hard limit of IPSec connections it is most of the time around 45 to 50 minutes.
You can check the files (with an active IPSec connection) in
for the limits. On a Terminal type
sudo more /var/run/racoon/*.conf
and you can see the content of the config file for the active IPSec connection, all lifetime values are 3600 seconds
lifetime time 3600 sec
The bug exists since a long time and is still present for example in Mac OS X Lion (10.7.3). There is a workaround (more or less) for this check
For Witopia it is easier to use the Mac OS X Client from Witopia