store apps are fine for multitasking, it suspends apps in the background if needed, although they still look like running in the app switcher, they resume just as quick as if they where still running so no issues with that (use 0.1MB RAM when suspended)
the only desktop ones I use are the free office 365, loads all these with no problem
I am very impressed how Win 8 works with devices with smaller RAM, not had any out of memory errors