I've seen some great studio work with an iPad rather than a tethered PC. The solution is still evolving as gains in bandwidth are offset by file size increases. One of the PPA instructors from Texas makes it a major part of his client work. Many commercial photographers in NY are using it so clients can immediately view images during a shoot rather than chimping on a DSLR. And navigation is intuitive for an iPad user.
Overall, it's a pretty good solution if you need or get value from immediate images. The JPEG's on an iPad look great - and certainly are good enough to impress a client.
There are a host of solutions with this approach. For an event photographer, event images can be displayed in real time. Even for sports you can get a lot of mileage out of stills viewed immediately.
For large files or RAW images, there are other solutions. This is really not a solution for RAW files - nor does it try to be such since there are bandwidth limitations of an SD card solution.