Since slashcode was, er, stagnating. The packages on debian (even debian-unstable) were ancient, and trying to upgrade caused a major problem with posting.
Wordpress puts out nice valid HTML, uses CSS extensively, has many fantastic plugins, and is much faster and less memory-intense. So far, they like it!
Downside? If you had an account before, it’s gone now. As are stock and zip codes. They aren’t going to be a portal anymore, but don’t worry — your information will not be sold. They still fully respect your privacy!
