BioWare revealed on the official Mass Effect forums today that the sequel would arrive on two discs, with the 360 version requiring  a disc swap at some point in the story.

“Even though there is a disc swap, it occurs at a carefully planned place in the game (that does not interfere with gameplay) and is done once,” stated community coordinator of BioWare Chris Priestly, “You do not swap back and forth. One swap and then done.”

The PC, on the other hand, will be a two-disc install

If you consider this disc swapping to be a serious problem with the game, then I would personally suggest going out and getting more exercise.