It would appear, that YUI (Yahoo! User Interface Library) is the "best" of the bunch, if a certain guarantee of cross-browser friendliness wishes to be achieved. Testing on FF 2.0, IE 7, Opera 9.25 and WebKit (on Nokia N95) - only YUI seems to work properly on all.
OK, so maybe there's a chance I introduced some CSS/JS bug somewhere, but my experience is YUI works better (than Prototype or Dojo) in most cases. I just wish it had Prototype's $() function.
OK - back to playing with Spring and Apache Derby,