I think it's generally a bad idea all around. Because Mr. Evil is eventually going to slip and do something pretty bad in front of his companions or one of his actions will be the straw that breaks the camels back; then he'll either be handed over to the guards, or they'll just take matters into their own hands.
So now Mr. Evil has to go to the trouble of creating an entirely new character, starting over with RPing with the group, etc. A pretty big hassle just for the novelty of playing an evil character.
I think actually I'd be more interested in why said player wants to play an evil character in a predominately good party. What does he hope to gain from this, other than (1) to create bad feelings when (not if) he does something that is counter to what the others want or need to do (2) or find his character incarcerated, banished from the group, or killed.
I'm sure there are some people out there capable of playing an evil character, but my own personal experience is that when a player wants to do this, I see red warning flags start to wave. More than once when closely questioned, said player simply wants a character that feels no constraint of law or morality, and 'can do what he pleases, as he pleases'. That way lies a quick road to campaign death.
I can see certain limited scenarios where it could work for a little while. Maybe two or three sessions (perhaps even longer, depending on what is going on), but then the jig is going to be up.
There are ways around it, too. The other characters can simply ignore what's going on under their noses (You know, Conrad always seems to be more than a little interested in lichdom. Maybe we should pay more attention to that book that Lilly saw him concealing in his pack the other night) but that eventualy is going to have alignment repercussions for them.
The question of his real motives and actions will eventually come to light, and it's been my experience that very very few players are willing to deal with the consequences. Detect Evil is usually the thing that reveals this. (I'm playing a paladin in the current campaign, so I've given at least a little thought to this.).
It doesn't have to be an instant death sentence to Detect as Evil. After all, that spell or ability can be fooled. It should signal you to keep a close watch on the person, however.