It's everywhere you look. Not only on the computer, but on flyers, shirts, signs - even restaurant menus. Sometimes it seems like the spawn of Satan, aka Comic Sans MS, is taking over the world.
I see Comic Sans being used everywhere, and it wouldn't bother me as much if it wasn't always being used for something that's supposed to look professional. It's suitable for something like a child's toy, not a job application or food packaging.
Unfortunately, I have come across many sites that use this atrocious font, which makes me want to pick up my monitor and throw it across the room (okay, maybe not...but I at least want to shield my eyes). What makes it even worse is the fact that it's usually in some neon shade of yellow against an aqua background. Or it's scrolling across the page at 90 miles per hour in size 72 bold. Even when it's at a normal size and a decent color, it still doesn't appeal to me at all. When I see Comic Sans I think of an annoying kid on an AIM chatroom saying "LOLZ HAI CHECK OUT MAH PICZO! MAH WEBBIE PWNS J00!" in hot pink. You don't want your visitors to think that too, right?
So if you're not in elementary school anymore, it's time to move on to a better font. There are much better default fonts out there - Tahoma, Arial, Verdana, and Georgia, just to name a few, so avoid using Comic Sans.