I'd been happily using Sabayon 5.3 for several months and loving it. I still had the rare Kontact and Konqueror crashes, but as said, fairly rare. I had updated the system using Sabayon's Sulfur a coupla times and had good luck with that until the last one.
It pushed KDE 4.5.1 down to updaters and while most had good luck with it - it brought my desktop down to a slow crawl. Then I put all the themes etc back to default and it slowed down to a stop. Turns out some other folks with NVIDIA graphics were having issues with the default KDE Oxygen components, but since I was already uncomfortable with the performance not using Oxygen I just booted my old install of SimplyMepis.
And I recall now why I moved on from Mepis. Kontact, Konqueror, and the plasma-desktop crash out quite often. Last SimplyMepis release shipped with KDE 4.3.4 and it was fairly unstable. I'm looking forward to the new release of SimplyMepis.
As an aside, I tried to use Linux Mint 9, but it had issues with NVIDIA cards too. I couldn't get a decent resolution on one monitor (let alone getting my dual monitor set up) and the NVIDIA proprietary drivers would not load - despite messing the (Resisted) Hardware Manager several times. The drivers from NVIDIA site wouldn't compile either. I didn't feel like messing with it much more. There were some posts on the Mint forum about it, but it wasn't a simple 3-minute fix and I had to get back up fast. That why I just booted my old SimplyMepis install.
So, I'm tickled to see the new Sabayon 5.4 release today. I'm gonna load it up at some point today or tonight and see how it goes. Cross your fingers for me. I might write something up on it if it goes well and I get some paying work done.