In 2007 I thought that my 8GB iPhone was as large as I would ever need. Two and a half years later and I've already filled up the 16GB storage of my iPhone 3GS. Enter AirStash, an expandable flash drive (via SD memory) that you will be able to access from your iPhone. Simply plug AirStash into your Mac, drag and drop some files to the mounted volume, and head then out the door with AirStash and iPhone in your pocket.
How the technology works is currently unclear (expect to see a demo at CES 2010), but a logical solution would be that AirStash automatically syncs its contents with an off-site server -- similar to what Dropbox does today. If it truly is as portable as that, it will obviate Dropbox's (and MobileMe's) need to install any client software if you are, for instance, using a friend's computer. Personally, I'd like to see Apple purchase Dropbox and turn MobileMe's cloud storage into something usable; but in the interim, I'm excited by the prospect that AirStash provides.