I agree with the comments that often when we know we've made a slight mistake, the audience don't seem to notice. The secret is to carry on regardless and not stop or draw attention to any mistakes - try to act like it was part of the plan! :-)

As for taking breaks, I prefer to have a short break if it's a long set, but sometimes, if the audience are getting into the swing of it, we like to keep going (I'm thinking more of pub gigs here, rather than concert type venues). As well as the ensemble numbers, we do a lot of solo or duo type spots within the band. This means that if you're not involved you can usually nip out to the bog or whatever, for a few minutes. Unfortunately I tend to be involved in most things, so I usually have to wait for a solo a capella song from one of the others, and we don't tend to do many of those in pub gigs :-(