The performance problem of dpkg on ext4 have been solved. Ubuntu has shipped a previous release of dpkg so that's why they had to document the problem. But in Squeeze, it's definitely fixed.
As far as default font goes, I have never noticed having ugly fonts by default. But then I run sid and only do installs in VirtualBox nowadays.
For Gwibber, it's a pity I tried to get the package updated but the release team was not open to allow a freeze exception. It's definitely useless...
For dropbox, we had a package in sid up to very recently. It got removed due to license problems. http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=610257
The package provided by upstream is built for Ubuntu and Ubuntu has bumped the epoch of the nautilus version which makes the package uninstallable, altough its content is compatible with Debian.