We normally do a 15 song first set, followed by two 10-12 song sets interspersed with 15-20 minute intermissions. The house seems to like the dual intermissions because its their chance to sell more beer, and we usually push the product as part of our patter. It keeps the publican happy and usually gets us invited back. Once you do take a break, you've then got the task of "recapturing" your audience. The message I get from all of the comments iher is that it is very, very situation specific. So, use your common sense, read the crowd as best you can, and, most of all, have fun. If you don't act like you're enjoying yourself, chances are the crowd won't have much fun either.