I ended up seeing "Mamma Mia!" (the movie) earlier this afternoon...
It was a good movie, but could have been - and should have been much better. Pierce Brosnan's singing "voice" did bother me, but I thought the director/editor made a very smart choice to not show him singing the first time he sang. You had to "think" if that was him singing.

Strangely enough, the casting choice I had the most issue with was Meryl Streep. I guess I've just seen her in too many of her "serious" roles, and it was just hard to accept her as a happy-go-lucky, somewhat carefree woman. Yes, the character of Donna has some "conflict", but there were times when I felt that Ms. Streep was trying to bring too much to the table. It was almost too "deep" a portrayal to me.
I also wanted the movie to be a bit more slicker. The filmmakers have made mention of the relatively small budget they had, and, alas, it shows. I was also a bit shocked and surprised to see that most of the choreography in the movie was just a recreation of the choreography from the stage show.
I did like it, but I found myself laughing a few times at the wrongs things for the wrong reasons. -And some of the plot adjustments just didn't work for me at all. Yes, there's a lot of "coincidence" in the original stage show, but at least those situations are set up (better).
Again, it was a good movie. But instead of leaving the movie theatre wanting to see it again, I left the theatre wondering when I could see the stage version again.