My attraction to Arch was that I wanted to run a fairly stable but bleeding edge distro. This would mean that I would be one of the first to notice any problems caused by the latest libraries. It also appealed to me that the distro is fairly 'simple'. That last point always seems to need some clarification. Arch is simple from the viewpoint that it is easy to get your head around how everything works together (and hence quickly understand issues if things do go wrong), rather than 'simple to install' for a new user, like say Ubuntu is.
I have enjoyed Arch since I switched and generally it has given my less problems than other distros I have used previously. I have had one or two minor hiccups after big upgrades but nothing that wasn't easy to resolve with just a little reading on the Arch forums or Wiki. Because it has been so straightforward I also switched a couple of other machines. My main home machine and a VPS/VDS that I use for various types of hosting and as a '$HOME away from home'.
Six months or so ago I decided to switch my home machine to something else. I didn't need the bleeding edge, 'latest and greatest' packages and I'd prefer not spend the bandwidth constantly downloading updates I didn't really care about. After a quick look around I decided that Slackware would be my best bet. It has its little quirks with regards to packaging that put some people off (though most of the so called 'issues' can easily be worked around if you care) and it only has a relatively small collection of applications in its main repository but neither of these things really bothered me. The key thing from my perspective was its strong reputation in stability and the fact that it shares much of the same philosophy of Arch in its approach to 'simplicity and ease of use'. Once again this is not really about pleasing users who are new, inexperienced or just want something that works 'out of the box' but rather about making it easy for intermediate/advanced users, or those who want to learn a little about how parts of the OS work together.