[vmacosta]

I've done this before with pretty terrible results, but my smaple size is pretty small. Here's a pokerstove which basically confirms that DeathDonkey is right in saying that you should usually be giving up unless it gets hu with the pfr.
Here's 5-ways and below it is HU vs. pfr:

Text results appended to pokerstove.txt

2,074,011 games 28.983 secs 71,559 games/sec

Board: Qd 7h 2c
Dead:

equity win tie pots won pots tied
Hand 0: 11.513% 11.46% 00.06% 237653 1284.50 { 4c4s }
Hand 1: 28.714% 27.66% 01.07% 573702 22229.67 { 66+, A8s+, KTs+, QTs+, JTs, ATo+, KJo+, QJo }
Hand 2: 20.474% 19.47% 01.02% 403872 21066.00 { 99-22, A2s+, K9s+, Q8s+, J8s+, ATo+, KTo+, QTo+, JTo }
Hand 3: 20.421% 19.43% 01.01% 402880 20954.17 { 99-22, A2s+, K9s+, Q8s+, J8s+, ATo+, KTo+, QTo+, JTo }
Hand 4: 18.878% 17.96% 00.93% 372554 19264.67 { 99-22, A2s+, K9s+, Q8s+, J8s+, A7o+, KTo+, QTo+, JTo }

Text results appended to pokerstove.txt

124,740 games 0.003 secs 41,580,000 games/sec

Board: Qs 7h 2d
Dead:

equity win tie pots won pots tied
Hand 0: 32.638% 32.64% 00.00% 40713 0.00 { 4d4h }
Hand 1: 67.362% 67.36% 00.00% 84027 0.00 { 66+, ATs+, KQs, QTs+, ATo+, KQo }