InVision looks to be extremely cool for the talented dual visual/UX designers who want to get slick looking prototypes out quick.
I recently used Axure RP for prototyping a lo fi interactive prototype for a craigslist redesign but ultimately I was really disappointed in the level of interactivity and the overall look of how the final prototype appeared. Later I used Flex to develop a higher fidelity protoype for a new interactive online shopping application but also found that styling the Flex app proved to be lacking in true artist customization.
Now, the only functionality I can tell that you can add is linking to other mock up which isn't exactly as capable as something like Axure pre-coding (which may be its weak point), but I think my favorite feature is simply being able to directly port a rather slick looking Photoshop, Illustrator, etc. mockup and make it function quickly as a lo-fi prototype. Often times it seems a client will be more interested in how it looks then how it operates (however unfortunate that may be...). InVision will allow the taltend visual/UX designer to create the look and functionality simultaneously into prototypes. Cool idea though in reality you could probably just create slices and quickly code some HTML to do the same. For the price tag, not sure I'd get it, but nevertheless a cool idea.
