I upgraded Regex Hero to Silverlight 5 today. The change is relatively minor overall. One of the biggest reasons for the upgrade is the increased usage of 64-bit browsers. And Silverlight 5 is the first version to support 64-bit browsers.
I fixed a couple bugs today. One was reported this morning about the scrolling when you hit the previous / next match buttons . The other was one I noticed where the replace textbox would trigger autocompletions in the regex box above it if you have an open backslash, parenthesis, or bracket. This was pretty annoying and I've changed it so the regex autocompletions will only work when the regex textbox has focus.