The current range of notebooks (especially the recently launched Intel Pentium M and Intel Centrino Mobile Technology notebooks) have more than enough power to handle most graphics and video editing tasks (provided you are not trying to create the next Matrix sequel).
Tablets are a no-no, cos currently, they are designed using lower-power processors. However, when tablets start using Intel Pentium M processors (as compared to Intel Pentium III-M processors now), then the performance will have a corresponding increase.
Notebooks subsystem (hard disk, mobo speed, graphics cards) will always be one or two steps behind desktops, but the performance difference is increasingly becoming smaller.