It looks like GPX is in Beta form right now. Points.com apparently takes a trading fee based upon the program you are transferring out of. The number of miles available to swap look like they depend on whatever individual users are willing to offer.
The trading fee varies by program as listed below. On top of that Points.com charges a $6.95 fee, which is currently waived. It looks like there is not much activity right now, so there aren't many trades available. Those that are appear to be at the 50 to 80% exchange rate (i.e. you lose between 20 to 50% in the swap in addition to the fees below).
Trading Fees for Alaska Mileage Plan are:
Number of Miles Trading Fee
1,000-30,000 miles $25.00 + $0.01 per mile
Trading Fees for American Airlines AAdvantage are:
Number of Miles Trading Fee
1,000-5,000 miles $80.00
6,000-10,000 miles $130.00
11,000-15,000 miles $180.00
Trading Fees for Aeroplan are:
Number of Miles Trading Fee
1,000-30,000 miles $0.02 per mile
Trading Fees for Frontier Airlines EarlyReturns are:
Number of Miles Trading Fee
1,000-10,000 miles $50.00
11,000-20,000 miles $75.00
21,000-25,000 miles $100.00
Trading Fees for Iceland Air are:
Number of Miles Trading Fee
1,000-30,000 miles $40.00