Sketchbook Pro doesn't seem to lag for me (maybe I don't draw quick enough), and that's primarily what I use the tablet for. I rooted and installed one of the mods to enable multiwindow on all apps. So, I use multiwindow to open up a picture (gallery or website) to reference while I sketch in Sketchbook Pro, Layerpaint, Art Flow, etc.
I also have a bluetooth keyboard and use Google docs. Same thing: I use multiwindow if I need to reference a website for something I'm writing.
But, I am perhaps not a typical user.. since I have am now trying out an Ativ Smart PC b/c I wanted to be even more productive (open up complicated spreadsheets, use more powerful art software, etc).