When do I need to splurge for a bartender? And is there any way for me to forbid him from wearing a bow tie and a black vest?

Hire a bartender if you're having 40 or more guests, says Debbie Barnes, a former caterer and the director of sales at Party Rental Ltd., in Teterboro, New Jersey. "You want everybody to have a drink as soon as possible," says Barnes. "It's something to hold on to that makes people feel comfortable." Having a professional behind the bar expedites service, eliminates messy amateur drinkmixing, and frees you up for more important things. The cost of bartending services varies by region: You can expect to pay anywhere from $15 to $25 an hour, plus tip. While the bow tie and black vest are traditional, if you're having a more casual event, you can politely but firmly insist that the bartender not dress like a penguin.