The main bug-fixes include - desktop integration and Raw image storing + some newly added languages.
Anyway, Ubuntu 10.10 comes with it by default (a wise choice :P) and if you have already installed it using the official PPA channel then you should receive the update. If you haven't then.. open your Terminal and enter the below command to install SHotwell 0.9.3 in Ubuntu.
sudo add-apt-repository ppa:yorba/ppa
sudo apt-get update
sudo apt-get install shotwell
If you use Fedora, OpenSuse or few other major distributions, then please visit this page for more information.