For the last couple of years, I've been commuting to work by bike come hell or high water, and we've had a little of both. It's about 7 miles each way, mostly downhill in the mornings on the way to work, and mostly uphill on the way back. It's gotten to the point where I just don't even think about traffic anymore, because it doesn't affect me; in fact, I can tune into my favorite podcasts and enjoy the outdoors, and it's one of my favorite parts of the day.
Aside from the price -- $2400 or so, although there's a 3-speed model in the $1800 range -- the other potential downside I'd mention is that, due to its 45-pound weight and somewhat awkward shape, it's not much fun to carry. If someone lives at the top of several flights of stairs and has to carry his bike up or down each day, the Elliptigo may be frustrating.
Elliptigos are, in short, the real deal. I've only been on mine for about a week, but I've retired my road bike from commuting, and I'm very optimistic about what this will do for my running and general fitness.
Updated: 12/7/11: Washingtonian Magazine did a review of the Elliptigo, and quoted me a few times.