I've been using Google Navigation for my last few trips to/from work, but I'd not used the Satellite Layer until yesterday, assuming it would struggle a bit over 3G whilst travelling.
Whilst it does struggle to download data in rural areas - as you'd expect - nearer built up areas it works perfectly, and boy, what a view! You get an angled view of your route ahead and it's kinda spooky, reminding me very much of a flight simulator, but with photographic scenery! Being a flight sim nut, this makes it even more fun for me :)
Here's a screenshot from the Google site - I couldn't take a screenshot whilst travelling, for obvious reasons!
It really is quite amazing, especially when it zooms in at junctions. It's like something you'd expect to see in a Sci Fi movie, but it's right there in front of you.
If you've not yet tried it on your device, give it a go, but watch those data charges if you pay as you go. On the 5" screen on the Dell Streak, it's incredible.