TCPMP's performance is dependent upon what you throw at it - this is true no matter what device you are using. In general it works fine with movies encoded for the PPC but will never perform like a 400 Mhz device.
The scroll wheel and trackball work fine as well. Again, depends on how hard you are using it - that is, the amount of dirt, etc. you expose it to. In 'normal' business & personal use, they have performed just fine in the few months I've had it. Trackball takes some getting used to though.
Hope this helps.
It has been my experience that the stronger an opinion is, the less likely it is to be based on or alterable by facts. - db