I get the feeling this part was missed by a good amount of people.
The one that springs to my mind is the 3DO. Bought it since it was the only console that had a Super Turbo port at the time, but I hated the damn thing. The load times were horrible and I never got used to the controller.
What are yours?
Current generation excluded as not to induce any flame wars.
EDIT: Just to stay on topic, I regret nothing so far. At least when it comes to console purchases.