I love much of what I see in the new PM!  kudos to the team!
Once I edit a set of photos, I use the simpleviewer export to generate and upload a web gallery so people can see my proofs.   So naturally, that's the first thing I tested in PM 5.  Sadly, by default, it generated a very different page that I'm used to generating.   I can't get the the thumbs and images do display on the same page, and the full size images are dictated, it seems, by the browser window size, rather than the size I specify.  I've fiddled with the settings, and they don't seem to make any difference. 
However (and I've not tested this) I'm psyched that PM & simpleviewer no longer require flash.  I get a lot of requests  to have my galleries visible on non-flash platforms. 
Ron