It's June 2013 and it appears that this problem has not yet been resolved. Skype just burns through my battery when the phone is on 3G mode; this issue also exists with SIP connections. Both Skype and SIP work great over Wifi.
As other posters have noted, this has nothing to do with 3G as the phone gets through more than a day and a half on 3G with Skype turned off.
This is a real dealbreaker