I never have...but in my re-run of Platinum I am seriously considering it. I have both a Prinplup and a Shellos in my team (that derp face...I HAD to have that derp face). Now. I know that Empoleon is steel/water. I have trained one before. But I really, REALLY want to put my Probopass back in my team. I already have two waters. The ONLY reasonable choice to box would be my Prinplup; all of its uses are covered by Shellos. Any others would throw off the balance of my team (it's still balanced on the merit that Gastrodon is part ground :P)
However, any strengths of the Probopass are covered by another team member.
It would serve only to be the thing you can't kill (unless you have a fighting-type 0.0)
Wrestling with it. Always feel obligated to raise the starter, starter is the best one to ditch for a rather racist jewtalian rock.