Is it worth upgrading my Lumix G10 to a Sony Alpha a33?

4/3rds lenses are expensive and thin on the ground. The Sony has a much wider range and takes all the old Minolta 35mm AF lenses as well. Don't forget that you have to multiply by 1.5 to get their effective equivalent though. A 28-80 will act like a 42-120 (35mm equivalent) on a Sony A33. The Sony has a physically bigger sensor than the Lumix which gives better images. The A33 has a fixed mirror too, so you don't get the blackout effect in the viewfinder when you take a shot.