Vince and the guys are wearing the same clothes from the first concert that they couldn't get into.
While walking to the U2 concert, Vince reminds Johnny that U2's Joshua Tree Tour was the first concert he saw. Vince said that he was seven and Johnny drove them. The Joshua Tree tour was in 1987, and the episode takes place in 2005. This would make Vince 25 years old and Johnny Drama at least 34 years old.
At the U2 concert, you can see Bono singing "City of Blinding Lights." This is one of the main songs in The Devil Wears Prada (2006) where Adrian Grenier (Vincent Chase) co-stars.