I wouldn't say we stalked too aggressively, but they were out there and we did try to quietly get close enough to photograph.  I had a 300mm zoom lens on my digital SLR, so it was fairly easy to get a few good opportunities.  When they have chicks with them they don't dive as much and they stay around a bit more.

We never get close enough to alarm the parents; or I guess I should say if the parents exhibit "alarm" behavior we back off.  We ease in very quietly, Neil does all of the paddling once we are close, and if I get the chance I am clicking away.  I miss a lot, and get a few, usually.