Aptitude's killer feature
I didn't like aptitude. Its user interface wasn't much better (IMO) than that of dselect (for the full-screen interface) and apt-get (for the command-line one); and it did not offer any features that I absolutely needed and couldn't get with (e.g.), debfoster. But it did require quite a bit more time to do stuff, since it maintains its own package databases, on top .
When installing rock again, I accidentally used aptitude one time, and found out about it's new feature (that only exists since 0.4.0, IIUC) which allows one to more detailedly specify what to do in case of an upgrade conflict.
This is really great. I've since completely switched to using aptitude, on all my systems—even the stable ones, which do not have that feature yet; the latter is mainly because it allows me to have a similar interface on all my machines, rather than having to remember how something is done on this box again.
Thanks, Daniel!