I’ve been looking at setting up some graphical models in QGIS recently using the tools available through the Processing option. I ran into some issues on my installation of QGIS 2.2 / Processing 2.0 on Ubuntu 12.04.4 64bit that I wasn’t able to recreate using the OSGeo4W install on Windows 7 Home Premium 64bit.
The problem was that I could build the models fine, but when I added in an output file for the model, the application crashed. Doing a bit of hunting around, this seems to be a known issue (see http://hub.qgis.org/issues/8716). It looks like a related bug report has been moved to a priority of ‘Blocker’ (http://hub.qgis.org/issues/6785).
So the way round the crash is to save your model with no name entered in the output field, then right click on the algorithm box and select edit (rather than double clicking to open that dialog). Add in the name of your output and save the model again. It should then all work as built.