Here are some issues I have run into running KDE4.4.3 on Mandriva 2010 (free):

1. modifying the address in Kaddressbook (or in Kontact) does not change the address displayed in Composer
2. clicking on "Reply" results in a new email that displays nothing of the original email but the Subject line. I can find no way to change this. (Adding %QUOTE%TEXT to "Settings/Composer/Templates" has no effect.)
3. Bogofilter with Kmail simply doesn't automatically detect spam. This may be a problem with the Mandriva distribution; but it worked fine with Mandriva using KDE 3.5.

And, incidentally, KDE4.4.3 with Akonadi takes 4 minutes to load; 3.5 took 90 seconds. Again, maybe a problem with my aging computer and its mighty 512Mb RAM but I can't afford a new one right now.

So I'll keep the computer running rather than shutting it down for ecological reasons, and use Thunderbird.