Implemented properly, there would be a pretty big penalty for the first widget, (about 300k to load the rendering/js engine), but each widget after that would take next to nothing unless the developer was an idiot and jammed it full of high res graphics constantly loaded into memory.
Edited to add: One of my friends seems to find it impossible to not respond to a text message, no matter what the situation that they find themselves in. It wasn't so bad before they got an iPhone, because the dumbphone's screen wasn't so large and bright. Now it's incredibly distracting at a concert, at the movies, at dinner, whereever. It's getting to the point where I'd almost rather not invite them out because they just can't avoid being rude with the ****ing phone.
That's not to say I'll never look at my phone during a movie, dinner, or whatever, but it's an isolated incident, not constantly. And if someone calls me, I either don't take the call or I get up and go outside. Sometimes I really hate technology. It's turned people into *******s.