I've been running KDE4 out of svn since pre-4.2, and it's really shaping up nicely. I actually finally built 4.3.2 out of Gentoo's package system last night, so I guess the 4.3.3 announcement was inevitable.
Anyhow, not sure if anybody's still sitting on 3.x waiting for 4.x stability, but if there is, I'd say to go for it. 4.x is really nice now.
Blog spam, no useful content, just ripped from kde.org with no link