Motorcycle GPS units

OK, this is a super-specialized question, particularly for a gaming board. But I know we have several motorcyclists and no shortage of geeks, so: I’m thinking of getting a GPS unit for my motorcycle for Christmas. Anyone use one? Impressions? I’ve zeroed in on the two purpose-built solutions, the TomTom Rider and the upcoming Garmin Zumo 550. The Rider’s been around a while and impressions, from what I can gather, are sort of the high-end of mediocre. The Zumo is new and I can’t find any really useful reviews. Anybody have one or can point me to real-world impressions (not just websites restating Garmin’s press release)? Are there other good solutions I’m overlooking? Weatherproofing is key because I ride everywhere and can’t schedule my trips around the weather.

Chet TV is interesting:

http://garmin.blogs.com/my_weblog/2006/10/chetv.html

Its got a standard jack so you can plug your helmet in for mobile coms, which seems great.