Perhaps the best all around filter out there!
I used this filter to supply water for 7 people (total) over the period of 2 weeks of backpacking in summer of 2011. The Platypus GravityWorks filtration system may be the best backcountry water filter system out there. It's light (under 11 oz.), fast (4 liters in 2-1/2 minutes) and flexible (you can carry up to 8 liters into camp). I use the GravityWorks clean reservoir as my hydration bladder, thus, eliminating the weight of my 4 oz hydration bladder (in other words, the GravityWorks is really only an additional 7 oz. to my previous pack with hydration bladder). Regarding filtration speed, this system is rated at 1.75 liters per minute (LPM), the same as the fastest pumping systems out there. And... while the water is filtering, by gravity, I can take care of other backpacking tasks - try doing that next time you're pumping 4 liters of water by hand! Lastly, with a 4 liter dirty reservoir and a 4 liter clean reservoir, you can carry up to 8 liters to camp (especially useful for nights where you're camping above a water source). This system is super-convenient for dispensing clean water at camp (i.e. hang the 4 liter clean reservoir and use outlet tube to fill water bottles, pots/pans, etc.).
Look for Platypus' ad campaign for this product in magazines (like Backpacker). All of their claims are true!
I have backpacked for over 25 years and have previously used First Need Deluxe, Katadyn Pocket, Katadyn Hiker and MSR Hyperflow pump filters. The First Need Deluxe and Katadyn pumps were reliable filters but required a lot of stooping and elbow grease. These filters were also fairly heavy. The MSR Hyperflow was light and fast, but was prone to failure (see my, and others', review(s)). Note: The Platypus GravityWorks system uses the same filter (hollow fiber technology) as the MSR Hyperflow but I have experienced none of the Hyperflow problems with the GravityWorks system. I'm sure success of GravityWorks can be attributed to its gravity operation and to Platypus' EASY instructions for quickly backflushing air bubbles out of the filter inlet (something you can't do, to my knowledge, with the Hyperflow).
I highly recommend the Platypus GravityWorks filter system.