I've had my iPad since the first day and have been playing with using it for many different things. Lately, there's been more and more "can I use the iPad to field review images?" questions floating around the Web and into my In Box. Now that Apple's shipping the Camera Connection kit, these have mushroomed.
My answer? The iPad is not quite ready for that sort of use.
First, if you're traveling with a laptop, I'd say the answer is an outright no. Using an iPad for initial review and culling just adds a workflow step, and right now, a slightly cumbersome one if you're using CompactFlash. I'd say if you've got the laptop, use Aperture or Lightroom in the field and get all your culling, metadata, renaming, and rating out of the way with a reasonably straightforward and seamless process. Yes, there are things I'd still like these programs to do for field use that would help me even more, but as one photo editor recently wrote: 3 photographers, 9 cameras: 25 captioned images sent by halftime of a playoff game via Aperture. You just can't have that kind of efficiency without using a laptop and highly productive software.
Even if you're not a pro trying to get images to press ASAP, a laptop with Aperture/Lightroom is still going to probably be a timesaver over just about any other process I can think of other than brute force archival (e.g. importing cards to a portable hard drive image importer and not doing anything with them until you get home).
The iPad, for instance, at first glance appears like it might take over that archival role plus give you the ability to review/cull. But the problem I find is that the workflow and software is cumbersome. Part of the problem is that the iPad doesn't really have a file system. Plus the Photo app that will "import" your images from a card is pretty minimal. The good news is that a product like Lightroom will recognize the iPad when it is mounted and offer to download any of the images stored in the Photo app. The bad news is that this really isn't much better than using a portable hard drive reader to store your images.
Memory (both kinds) also comes into play. You've got a maximum of 64GB of image storage (and it's going to be less than that if you've got any other apps or media on your iPad, which I'm sure you will). And you've got a maximum of 256MB of RAM. Those two things taken together have implications for a prolific raw photographer: this isn't the platform for dealing with raw images in its current configuration.
Some help is on the way. If you've got an Eye-Fi card there's an app called ShutterSnitch that can act as an ftp server and directly download your JPEG images as you take them and allow you to browse them. But the program needs much more capability to make it fully useful to a serious photographer, I think. Moreover, I worry when I see mismatching marketing messages for a program. One of the touted features is the ability to "warn you" when an EXIF parameter like shutter speed is outside an expected range. On the other hand, they tell you to hand your iPad to your client so they can get a good look at what you're photographing. Great. So these two things taken together mean: client knows when you're making mistakes! So we turn that feature off and...well, we don't have many other features, so we're back to just a browser again.
As much as I enjoy my iPad, I've yet to find a photographic usage that I'd carry it on assignment for. If I need backup storage, I'll use a portable hard drive image importer. If I need to cull, rename, rate, and caption images I'll use my MacBook Pro. If I need to know the sunrise time or location, I'll use my iPhone.
This, by the way, is one of those "third device" complaints. There was much speculation when the iPad was announced that there wasn't really a useful portable device between a smartphone and a netbook/laptop, and that no one would carry all three. I think that conclusion is somewhat wrong. For many uses--such as a prolific, serious photographer--it's certainly true that we wouldn't carry three devices into the field with us, at least with the software and storage we have so far. But for other uses, I'm pretty sure that the iPad becomes either "the one" or "one of two" devices many people carry.
Bottom line: the iPad needs expandable storage (removable SDHC cards), more RAM for applications, plus applications need to get more sophisticated and workflow friendly, before it becomes an indispensible photographer's gadget.