Tom Petty at the Marcus Amphitheater was the best show of Summerfest 2010. He has no fake backing tracks, his drummer doesn't use triggers, and Tom Petty actually plays guitar when he hits the stage. I can't say the same thing for someone like Justin Bieber, but he performed at the festival too.
ZZ Top was solid, and could have been a headline act at a side stage. Speaking of side stage, DEVO at the Miller Lite stage was awesome. I loved it when Boogie Boy heaved hundreds of super balls out into the crowd. The band was tight, if not solid.
The Summerfest grounds and Marcus Amphitheater are not dark yet. There are the ethnic festivals, and one off shows to come. See you at Summerfest 2011.