Is it OK to check your spouse's cell if you think they might be cheating?

I just read a post by Gatsby about discovering his wife's infidelity through checking her text messages....I have been thinking long and hard about doing the same thing but its such a privacy violation I can't bring myself to do it.

I'm really curious what both sexes think of this.  Assuming you already have reasons to suspect your spouse of infidelity, is it OK to check their text message/emails/IM?

It seems like a really harsh thing to do -- what if you find nothing?  It doesn't prove anything if there's nothgin there, since most people have the sense to delete stuff.  But on the otehr hand, it's no crime at all comapred to what you are afraid to find.....