I set up GUIMiner as shown in the tutorials, and ran it, and it gets stuck at "Connecting..."
It did this for an hour until I decided to click "Show console".
Show console kept looping at "Line:" for a few seconds, and then the program crashed.
I looked at the guiminer.log file, and it was over 1GB; all of which was just a timestamp, and then "Line:"

Any idea what could cause this?

Same here, exact same problem.  I have attempted connecting through slush, deepbit, and btc mine.  Same problem every time.  it says "Starting..." in the bottom right corner, and remains so for hours.  solution?

Same here, until it suddenly said "connection problems" after i did a start/stop, and then it started giving me figures for the CPU - i still have the problem with the cuda worker on the same computer :-/  - Was starting to think it might be the gpu it failed to connect with or something.

Makes me miss the RC5 challenge

Same problem here.
Attempting to connect to slush's pool without success, just stays at starting for a bit and then connecting.

CPU Usage for the process stays at about 25%.

Console:
Listener for "Default" shutting down
Running command: poclbm.exe --user=***** --pass=***** -o mining.bitcoin.cz -p 8332 -d0 --verbose
Listener for "Default" started

OpenCL is also not detected, although a GTX260 is installed with the latest drivers.