According to a sort-of PSA starring Austin's "mayor" (a suspiciously tanned and elaborately mustachioed Kyle McLachlan, who also plays Portland's mayor on the show), more important than spotting the good stuff is avoiding the bad—namely, strollers and "intimidating" cats. (Which apparently leaves out Maplewood.) Bars, coffee shops, record stores, cool people, seemingly mostly in South Austin: all tops.
Portlandia co-creators Fred Armisen and Carrie Brownstein no doubt know of what they speak. Brownstein, who plays "Carrie" on the show, lived in Austin while writing her memoir, Hunger Makes Me a Modern Girl (she gives a shout out in it to sometime-Austin hotelier Liz Lambert for providing a space to write in) and during her band Sleater-Kinney's recent Stubb's concert gave Austin props for "being so much like Portland."
Austinites wanting to know delve further into the subject of its cool neighborhoods might want to check out Portlandia prequel (not really) Slacker (1991) or its New Austin update, Slacker 2011, for more info.