Having this problem now with SlimKat 4.4 RC3 2.8 for samsung Galaxy S i9000 (trying to upgrade to official 3.0)
It refuses to detect that its connected to a computer. Have to reboot several times to get it working, and once it works, it only works for a short while. Then all of a sudden, connection dies.
I suspect it's the low memory condition that causes this. Slimrom has an extremely aggresive memory management, and some important services, such as bluetooth, usb connection, wifi etc...etc... is killed due to low meomory condition.