As the name would suggest it's all about storage, but not just for the standard slew of files you'll see supported on sites like Flickr or Google's Picasa. Instead, SmugVault is all about the files professional or advanced users end up with, like the RAW and TIFF files from high-end digital SLRs, and the PDF and PSD files from post-processing.
The service is tapping into Amazon.com's S3 cloud storage to serve up all that space, and offering users an unlimited amount of it as long as they're willing to pay. There's a re-occurring $1 charge per month, alongside 22 cents per gigabyte and charges every time you transfer data in and out. In consumer products like Box.net this fee is usually eaten by the start-up or subsidized through a premium plan. Smugmug's hope is that the a la carte model will appeal to the folks who don't fit into segmented plans from other providers.
However, the real appeal of putting all your files in SmugVault may be that it uses the same visual file browser found in SmugMug. This means you can sort through your photos and videos in a familiar interface. There's also a built-in system to keep you from downloading duplicate files (even if they're different formats) by putting them together by file type.
One thing to note is that potential SmugVault users must have both a SmugMug and Amazon account. SmugMug is only serving as the front end to Amazon's S3, so all of the billing will be done by Amazon. As Allen over at CenterNetworks notes, this is likely going to end up confusing folks who want to keep their paying Web accounts consolidated.
The only upside I can see is that I'd rather Amazon have my billing information than yet another start-up, even if it is one that's been profitable since launch.