Hi pistoriusp, Peldi here from Balsamiq. I'd love it if you could send me an email (peldi@balsamiq.com) with more details about the sluggishness you have found with Mockups. Preformance tuning is a way of life and I constantly make little improvements, but having a set of files or steps that are still slow even in the latest version http://www.balsamiq.com/products/mockups/desktop#download would greatly help me in finding and fixing the bottle-necks.

Thanks!