Self-entertaining Dogs

I'm having a pretty lousy week, so none of the sixteen or so (seriously) draft posts I have are going to get done tonight. In the finest tradition of the bloggers I've been reading for years I'm going to recycle some content and then beg for comments. Bare with me though, I think this could be kinda cool.

Consider this video that I posted over on my DSF blog:

Buddha has a amazing ability to occupy himself. At home he actually "asks" to be put in his crate with a squeaky toy at least once a day. (Gage takes any loose toys away from him. He's a bit of a jerk that way.) Every Sunday, before we start classes he will run in circles and literally throw a tennis ball to himself. (It's very early on Sundays, and I promise I'll remember my video camera one of these weeks.)

Also consider this video> of Pia Silvani's beautiful girl, Lena.

Lena was have a blast occupying herself with a squeaky bear toy she found in class today.

What's your experience with dogs that will play alone? Is it common, or something you see less often? Is there a particular personality type or breed that it seems to be more common with?