I'm current having some small problems with SMPlayer in Ubuntu 10.10. I'm not sure what the cause is but I'm fairly certain it relates to the recent switch to Kernel Direct-Rendering-Management (DRM) and Nvidia drivers. I say this partly because I am noticing other small video glitches but for the most part they are not worth even mentioning.
However specifically there seems to be problems with trying to use VDPAU. (If you don't know what that is, in a nutshell it is letting your videocard's CPU, often called a GPU, do video playback/decoding for you, which is faster than using your main CPU as well as leaving the system CPU free for other tasks.)
While the problems with VDPAU are hard to pin down (I'm having trouble finding an exact bug report to list here), I have found a small fix to help with my other SMPlayer problems.
I have started using daily compiled MPlayer packages from this PPA.
It seems to have helped with smoothing playback in other areas where I might get lockups when I would use some more exotic SMPlayer/MPlayer feature.