It's quite quick on my iphone 4 but the actual maps are blurred. It would seem that they are rendered at the "old" iphone resolution. This gives the app a very unpolished look unfortunately.
Yeah, it's blazing fast for me; I don't understand the hate in the other comments. Unlike Bing maps, getting directions is intuitive for me, and I couldn't care less about satellite imagery. If caching works at all, this will be a useful app. Guess I will have to give it a week or so for evaluation, though.