Once was a time Microsoft were very stingy with how big a game downloaded from Xbox Live Arcade could be. These days, though? Don't worry about it, publishers, knock yourselves out.
Old-timers on the 360 front will remember a time that Xbox Live Arcade games had to come in under 50MB. That 50MB was then stretched to 150MB. Then 250MB. Then along came Portal: Still Alive and Street Fighter II HD, and it looked like Microsoft's restrictions were bending.