It isn't that bad... But it isn't that good, either.
The huge problem is that some apps (file manager type Konqueror, Dolphin) are terribly slow. Copying files using the fish protocol failed (used sftp instead). The amount of customizability is lacking for KDE.
I hope 4.2 fixes these issues. I have high hopes. I like the idea of Plasma, but it is just too rigid right now. Most things in KDE are.
2014 is going to be a good year. More content, more streamlining. Be a part of history!