It won't work to just bulk convert to PV2012. You have to re-develop,
however, once I figured out the new controls the results are much better.
Victoria Bampton has an excelent post on her blog
http://www.lightroomqueen.com/2012/01/18/pv2012-develop-sliders that
explains how to work with the new controls.
PV2010 is good and PV2012 is better. But the translation from one to the
other is not so good. Make a snapshot, convert to PV2012, reset all
settings except maybe color balance and crop and start again using
Victoria's instructions as your guide