StarUML is just really slow for me.
This might come down to using web technologies for the program and me not using my best PC but it's still not slow and I think a computer that can run Photoshop without any hassle should be able to run a UML diagram software.
However, a usable performance would definitely be a killer feature to actually buy StarUML.
the program only run smoothly in linux machines
Really really laggy on Windows PC with i7, 2GB NVIDIA and 12GB RAM even with small projects!!!!!
As @Florian Reuschel said, a PC that run intensive tasks (Photoshop, premiere pro etc.) should manage very well an UML software like StarUML!!!
Well it also feel sluggish on an i7-2600k. So i guess it just due to java script. a Bit sad as it would the best UML diagram app in the world if it didn't lagged so much.