The Twinkie of musicals, 'Mamma Mia!' arrives at National Theatre, somehow not totally stale

Only about a half dozen shows have run longer on Broadway than "Mamma Mia!," which will disco past "Rent" this week on the all-time durability chart. It still tours, too, and a non-Equity company is at the National Theatre this week, camping it up through the musical's catalogue of ABBA songs.