I've always been a bit skeptical about Eagle Creek's Pack-It cubes. This may spring from the fact that as a travel writer, I identify more with the stance of A Perfect Mess rather than the hyper-control of Getting Things Done. I've got a pretty good packing system down with rolling and stuffing and I manage to make a lot fit into a small carry-on bag.
I used these packing cubes on my last two trips though and have to say that while I didn't fall in love with them for packing, they do make repacking a lot easier. I also didn't unpack at home and go, "Oh that's where the last clean pair of underwear was!"
These Pack-It cubes come in a variety of shapes and sizes. I used a two-sided half cube that's sized for socks and underwear and a regular two-sided cube that's good for rolled shorts and T-shirts--or dirty and clean laundry separation. The items feel rugged, with good zippers, and both these models have mesh to keep the air circulating.
Since I was pretty much living out of my bag on both trips, the biggest benefit of the cubes was to keep my bag more organized. No trouble finding what I had packed and not so much mayhem inside the pack.
So if you're a neat freak, these things will enable you to indulge your obsession no matter where you travel. If you're a total slob, these cubes will help you get packed up and out the door faster when it's time to move from one abode to another. When you're backpacking on the road for months that could add up to a lot of time. If traveling for business, well, time is money.
Eagle Creek Pack-It Cubes are available in about 10 different colors and patterns from Amazon, Backcountry.com, REI, and Magellan's.