Sure it is. I'm running it on my laptop, and I can't really see any major
issues. I think the complaint about KDE4 not being "ready" is about KDE4
not being identical to KDE3. Well, it will never be.
It's like the complaints about GNOME2 vs. the "old GNOME". Or OS X vs. Mac
OS9. The change was substantial, and people complained. But in the end, the
result was a system that was clearly superior than the old.
KDE4 is now 10 months old. 10 months. Give it time. It's growing fast :).