Does iPad 2 3G's GPS work without SIM card inserted? I own an iPad 2 with 3G but I've not inserted SIM card and I'm not planning to unless it's really necessary to get GPS working. 

I was wondering if iPad 2 3G can navigate without SIM card (thru Navigon for example)?
Yes for products that have off-line maps (Navigon and Tom-Tom for example) you don't need a connection.

Some add-on services (e.g., Tom-Tom traffic) will need a connection.