Arch is one of the most modern distros out there.
Arch is the dream that some i686 Debian users have. (if only latest GNOME/KDE was working with apt-get, if only I wouldn't have to wait for 3 years to get sth to stable, if only..)
So Arch is good for debian users that want to live in today. [i like debian don't worry] but I like my desktop-use with X server too.
Arch is for you if you 're starting to hate GCC after leaving gentoo half the day compiling on KDE/GNOME or other HUGE package..
I was a slacker. Arch does what it says and does it with a binary-based package system that has dependencies. So imagine Slackware [modern software, STABLE, fast, not taking too long] with dependencies and you have ARCH LINUX!
after going to Arch I never looked back [especially to Gentoo/Debian]
those two distros mention above, are very good. But as a Desktop GNU/Linux user I wouldn't recommend them except you're a gcc-crazy guy (gentoo) or a searching-for-debs-that-one-day-will-work guy (debian)
SLACKWARE is always in my heart
ARCH LINUX is always in my HD