<half-rant>
I use Debian on my other boxes. I chose Arch Linux ARM for the DockStar because I've always had mixed feelings about Debian's release system.
With Debian you either have to accept to run an outdated system (stable), or the chance it might become partly broken. Stable tends to be only mildly outdated when it's just been released, and testing tends to be worse at the same time, stable gets older and older and testing gets progressively better.
Sometimes I need to upgrade some app and I can't because it has a huge load of dependencies, typically standard libraries, and if you give up you enter the no-man's land of a mixed system (= you're on your own); backports should address this but AFAICT there are not many backports right now for squeeze. Or some really important package (i.e. nvidia-glx) gets dropped out of the repos for some time and you have to install it manually and that goes against the Debian Way, have fun with that.
Debian's release cycle tends to be long (I would say too long), hence the time during which stable is outdated enough but testing isn't too much work tends to be non negligible.
Pros of Debian are: packages are many more, tend to be of higher quality if you take into account AUR (which to me is a necessary evil exactly because the official repos are not as rich as Debian's). Also Debian has more work already done for you (less time wasted on menial work is good for me), but I feel this is a minor issue on non-desktop systems. There also also many third-party repos which have very high quality standards, and being one of the most popular distributions, .deb packages are easy to find.
Of course there are exception, like the OpenSSL fiasco or the fact many Debian packages are stuck in ancient history either because the maintainer has vanished or because for some reason he has decided it's a lot of work to make the new version fit inside the framework Debian chose to use.
Arch focuses on some sort of minimalism that sometimes just appears to be for its own sake. I think being somewhat more pragmatical would just benefit the end user. Take for example, Debian's policy against closed source software but then again you have the non-free repos to save your ***** - that's a way to state your principles and yet not leave your users out in the cold having to fix things themselves.
Then again Arch is more for hardcore Linux users, so this way of thinking works up to a certain point. Beyond that point we start questioning some choices of Linux users and their attitude so I'll keep those thoughts to myself.
I'll stop here, I'm sure there are other differences but this post is already too much of a rant
</half-rant>