Slowness in sales of tablet PCs means nothing to many happy users, however. For example, at the Altoona, Wis., police department, two Lenovo ThinkPad X41 Tablet PCs have been in use inside police vehicles since 2005, and the department is planning to add as many as 15 newer models in the next year, said Officer Dana Brown, manager of the department's technology initiatives.

"There was a $200 premium over a standard laptop, but we wanted the versatility, and it has definitely paid off," Brown said. "We're getting away from the keyboard ... Tablets are more than a niche for law enforcement."

Proponents aside, here are eight reasons why tablet PCs haven't moved into the mainstream.

1. The price is too high.

Compared with a typical laptop, a tablet PC can run from $200 to $300 more, meaning most tablet PCs run from US$1,200 to $1,800, depending on functionality, Fiering said.