Computing Pet Peeves?

Matthaeus asks: "I'm a 3rd-year CS student who will most likely be writing end-user applications after graduation. Naturally, I would like my apps to sell well, so I want to minimize user annoyance as much as possible. In an effort to improve my coding skills, what are Slashdot readers' biggest pet peeves when it comes to software? For example, my largest pet peeve is when a program steals the focus from another program while I'm typing. Maybe other software developers could take notice of this discussion also."