I bet you take your thumbs for granted. I know I do. You know how I realized this? I sprained my thumb pretty decently on Tuesday during my ultimate frisbee game. Right now pretty much half of the inside of my palm, my entire thumb, and the outside of my thumb area is black, blue, swollen, and sore. Moving my thumb (in the limited amount of range that the spraining allows) doesn't hurt at all. It's putting any pressure on it that really doesn't feel so nice.
I didn't think it would be a big deal, but even little stuff like typing this post is different with a thumb out of commission. Pounding down on the space bar or using my thumb for the usual keyboard shortcuts I'm used to isn't going so hot, mostly because I have a very firm keyboard. It's hard to adjust your typing pattern to accommodate the lack of use of a thumb.
Going to the bathroom is fun. Undoing buttons is a horrible pain in the ass. Attempting to put on pants doesn't work so well. Grabbing a can of pop or a glass has to be done with the other hand. I had to switch the hand I eat with. Thankfully it's not my throwing hand so I can still play in my ultimate game tonight... although catching things is going to be a bitch, isn't it?
Anyways, the moral of the story is don't injure your thumb. It really blows.