Our Sales people manage subset (via custom export) from our Marketing database of some 50-60,000 contacts I would estimate. so they tend to keep about 5k contacts apiece at any one time. (we found that to be the magic number that would cause a 16MB handheld to melt down in our case). An administrative assistant that makes sure each rep has the contacts he or she is most likely to need (changes all the time).
It seems like overkill, but we recouped enough extra sales after the first month to pay for all of the blackberrys, service, and the BES server. so it clearly works. Despite the naysayers saying it is simply not needed. I know most of the increased sales were due to push email - rather than a push of 5k contacts - . But every little bit helps.