With other gadgets based on Maps, it can be even worse than badly centered content, like with this iGoogle gadget that use Google Maps to track satellites in real-time: http://www.google.fr/ig/directory?type=gadgets&url=www.n2yo.com/sat/gsat.xml (this gadget has always worked flawlessly in Google Wave and was also working perfectly in early versions of WiaB demo servers).
When loading a wave with this Satellite Tracking Tool gadget (added via its http://www.n2yo.com/sat/gsat.xml URL), because the gadget container size isn't set yet, the gadget (or is it Maps?) apparently detects that there isn't enough room to display a map and simply display a grey background instead, thus totally breaking the gadget functionality.
If you reload that same wave enough time, you may end up having a slowdown (is it on the WiaB server side or on the XML gadget hosting side?) that will make the gadget load after the gadget size is set. In those rare case you'll see this Satellite Tracking Tool gadget working flawlessly, proving that the gadget isn't faulty, but defeated by the container width loaded to late.