I modeled my original Excel sheet and much of what I have in the Low O2 sheet after the menus, navigation, etc of ProMash.
There is zero content in BeerSmith that should sway the average ProMash user. I'm an Excel guy to the end and I can import beer.xml into excel as well as output.
There is nothing done in BeerSmith that isn't done more elegantly by ProMash or an Excel sheet.
To Denny's point, there is no easy or elegant solution to the PM -> BS xml issue. The directories in particular are going to be a lost cause. Your best bet is probably to take a day to manually port everything in.
Why did you stop using ProMash btw?