Concur with the above.

The only place I've had a problem is JFK, where there is nothing at the UA terminal (closest is DL). We 'suffered' for 30 minutes one morning. Other than that used CO at LAX (worked out better as our UA flight to BOS was two gates away!) or RCC's (either via PP in BOS or because of C classs ticket).

If you don't go through UA hubs alot, it could be a good alternative.

In the UK, if you have Amex Plat or Centurian, it's FREE!

Oh, other downside, you do have to pay for guests (about £15, 25-30 US Pesos). Though sometimes, they don't process it