[bobgreen]

I believe it is appropriate to play when the pot offers a slight underlay for two reasons:
Some opponents, who are not cognizant of the pot odds that almost justify your call, will think you are a dummy; and
Other opponents, who are not cognizant of the pot odds that almost justify your call, will be encouraged, in future action, to try longshot draws because you have shown that it is OK to do that.
Bonus reason: The guy you beat might go a little tiltish