I recently helped a friend set up on online psychology test. Not being at all familiar with psychological experiments I was directed to an existing software suite for inspiration – PEBL Test Battery.
Although GWT makes it so easy to write web applications it doesn’t help you follow any design patterns (e.g. MVC or MVP). I used GWTP to implement a Model-View-Presenter front-end (following an MVP pattern with this framework is much easier and it’s well documented). Although GWT now has an API to handle HTML5 canvas it doesn’t seem to be documented anywhere (well I couldn’t find anything other than Javadoc). So I used Vaadin’s GWTGraphics library which is well documented. I think it’s also more cross-browser friendly (or, to be more precise, it fights all the different versions of Internet Explorer – Microsoft like to keep themselves and everyone else busy).