When I first set up my wireless connection, I had problems getting my encryption working. So I left it open and figured I'd deal with it later. There are so many wireless connections in my building that I stupidly thought that everyone who wanted one had one. Today it finally dawned on me to check and, sure enough, someone's been using my open wireless. Shame on me. It took me about half an hour of futzing around with it, but I finally locked it down.
Now my connection's no longer dropping and the Intarwebs are faster than ever!