Depends on who I am playing, sometimes I play music or sometimes there is nothing at all I just use it so my opponent won't try to talk to me or to drown out the loud railbirds. Only during local tournaments do I find myself using it because people are "familiar" with you and so they talk to you between shots, from the rail or otherwise when you are trying your hardest to play the match seriously even though they aren't.
Out of town I don't wear it because it's usually a decent sized tournament, like KF Tour or SE Open, and people are respectful of not intentionally or unintentionally sharking you. Never thought about it till now but it's my friends that I try to avoid listening to/talking to during a match, I try to play every match hard so talking isn't something I do. When someone says something I
Since I am very easily distracted I try not to talk or carry on a conversation because I will then want to talk and not focus on playing, so I know it sounds rude that I want to drown out my friends talking but I am doing it to avoid my weakness. Maybe if my concentration was better I could talk to them all I want between shots then get down on the shot and be able to focus 100%.
Also I only wear it in one ear 90% of the time, the only time I wear both earbuds is when I am playing someone I really dislike, I think it's a good compromise to the arguments that people post about not liking Ipods.