Supposedly, the Xbox 360 will be getting a "huge" update at the end of May.
According to the folks over at Xbox Archiv:
""We got confirmation from Boris Schneider-Johne that a huge Dashboard Update will arrive at the end of may! It will feature a Download manager for 6 parallel downloads in the background. He also mentions that there will be a lot more features in there but it will be a surprise and he won't talk about it! The downloads will also running while a game is played."
I don't know how reliable Xbox Archiv is, but I like what they're saying.