We usually go in September, too. Knowing what you want to do is important. If you want outlet shopping/dining, you're still good to go in September (thou some stores alter their hours, closing sooner in September during the weekdays). You should still be able to get your shop-on in early-mid September without issues. During the weekends (Thursday night thru Sunday/Monday afternoon), you'll still be dealing with horrendous crowds and traffic, both at the outlets and the beaches. For the most part, boardwalk activities (Funland, haunted house, arcades, specifically) shut down after Labor Day, and only open during the weekends. I get the feeling this is a changeable thing thou, relying on expected crowds, something that's changeable based on events occurring in and around Rehoboth after LD). If you have children hepped-up for boardwalk attractions, they may be dissapointed. If you don't care, or are an adult couple looking to get away for a quiet weekend, then post LD Rehoboth might be your cup of tea. We like it then and can often find things to do that don't involve the boardwalk: Bike rides through Henlopen state park and downtown, fairly lively night life on Friday's and weekends, the art colony in Henlopen acres, and just milling about surrounding towns like Lewes, Cape May, Milford... there's lots to do, but many things summer visitors might take for granted during the peak season will be harder to find open, even thou you'll still be dealing with about the same level of crowds around Rehoboth proper and the outlets (slightly less people on the beach itself if the weather is at all chilly). Rehoboth has events happening all year round (ie. Halloween fest, Christmas tree lighting, art shows, film festivals, etc.); it just depends on what you're looking to do.