I have tried 4 different sets of headphones:
Sennheiser HD429 Over-Ear Headphones
ipod ear buds (3rd gen)
iPod ear bud (4th gen)
Sony MDR-EX15AP EX Monitor In-Ear Headphones
All only get sound in the left earpiece.
I have also found that a friend has bought exactly the same model notebook and has exactly the same problem. Lucky for them they will only need to use the headphones very rarely.
They did say that they were told by a "tech" that the solution was to pull the jack out half way. GREAT solution if you want to spend hours holding it there so that it won't fall out completely, but at least you do get sound in both ears, although a bit crackly.
All I have to do now is learn to play my drums, harmonica and guitar with just one hand!
BTW it was really hard not to laugh in their face when they showed me the "solution" that the "tech" person told them was a fix.