I'm still in the "live in winter" camp but I agree that transition season is rough. I'll run in slush if I'm not damaging the trails but sometimes I bail out and run rail trail, gravel road or even treadmill at this time of year. As mountain bikers, we are also itching to get onto the trails but we have to wait even longer than we do for trail running. Sometimes we drive down toward the city and ride on their network of paved paths. It's worth it to have a good XC ski season though, right? Right?!? ;)
May is not a bad bet, especially if it's shaded! We have quite a huge pile in our tiny yard thanks to snow falling off the roof, I think we'll have a little glacier for several more weeks. Even the open fields next to us still have knee-deep snow (as I discovered this morning when I tried to take a "shortcut") despite having zero shade and no extra dumpings.
I've been moving more into the "visit winter" camp each year. I love skiing but I can live without it, which means I can live with only doing it on a few select trips per year. Having trails to run on, though... that's nice to have all year round. Hmm, where do I know of that has awesome trail running year-round?