I guess it depends on what you're used to and what device you are coming from. As someone coming from Android (Evo), I think Bing Maps is nowhere near as robust as Google Maps with Google Navigation. Sure, Bing Maps works fine, is nice and smooth, and Telenav is actually a decent alternative to Google Navigation... but the nice integration that Google Maps had with all levels of Android cannot currently be replicated on WP7. Add to that the fact that the Bing Maps basemap is severely lacking when compared to the Google Maps basemap (see
here for detailed analysis - there's actually a ton of great content on that site re: bing maps and google maps and web mapping in general) and I'm firmly in the "Bing Maps is fine but not great" camp. I'll probably like it more as I get used to it (and as I use it more; frankly, I haven't used it much since getting my arrive).
What I'm REALLY looking forward to, though, is what happens with Ovi Maps on WP7. I've been playing around with maps.ovi.com and I'm pretty impressed. I'm excited to see what happens with this Microsoft/Nokia partnership. It just seems to get better every time I read about it.