What 256MB of Ram Means for Developers and Users
Background tasks aren’t meant to provide apps with core functionality in Mango. There’s a hard limit on 10 background tasks that’ll cause the 11th+ background task to fail, and users can capriciously turn background tasks off.
-- Justin Angel
What does this mean for users?
Users will likely not notice much of a difference, until it comes to the 11th task. Even then, Microsoft has found a nice way of letting users know they've reached their Background Task Limit by taking them to the background tasks page in settings.
What does this mean for developers?
Most likely, developers will end up spending some time adjusting apps for each memory set (at least those who are concerned about having their apps run on ALL Windows Phone devices).
Of course, all of this is just a temporary problem, as Windows Phone 8 "Apollo" will likely bring more memory and greater background task capabilities with it to Windows Phone devices.
UPDATE: I've added this video from Mobile World Congress 2012 on the Nokia Lumia 610