From my first readings of SR4, it seems to me tht most people in the 2070's would be constantly bombarded with AR messages and information; this seems to me as a vast load on the Shadowrun 4e GM. So how do you trim down this stream of information and successfully GM the AR experience?

generalise a situation, occasionally mentioning a funny ad, or something the char might like out of the spam etc, and then highlight the info the chars actually want.

You've got to think about it this way. To someone from the country, a visit to the city can be very overwhelming, with noise, smells, people everywhere etc. It would be a very distracting sensory overload to them. But to someone who lives there, it's just another day. They filter it out unless something unusual happens.

AR would be just the same. To your average Joe who uses it everyday, it's just background noise. They notice something unusual when it happens, or when they are specifically looking, but otherwise it gets described in much the same way you describe the unending sea of people and cars that surround someone in downtown, ie you mention it's there, then forget about it unless it's important