This Boston trio sports two acoustic guitarists, a skilled percussionist, and soaring vocal harmonies. Their concise songs tend to take up residency in your head, thanks to melodies as catchy as commercial jingles and an unpredictable array of subjects that seem to traverse effortlessly from heady and heavy to lighthearted and humorous. Champions of the "street team" ethic, Guster have built up a large following by letting fans do much of their promotion through a "rep program" in which volunteers distribute fliers in advance of shows. They've also built a legion of hardcore disciples via the Internet and engaging live shows known for the band's witty and interactive banter.