I used to do 3000miles but once switched to Mobil 1 I go to 5000 miles. It's a struggle to keep myself from dragging the Topsider off the shelf as the odometer tells me it's been 4000 miles and the oil looks pretty dark.
I try to remind myself about the Consumer Reports article about 3-4 years ago on oil change intervals. They took NYC cabs (talk about "severe service!") and had some of them do 3000 mile change intervals and some do 7500. They tore the engines down after (I think) 50,000 miles and found NO DIFFERENCE in varnish, sludge, cylinder/valve train wear, bearings, etc.