The secret of the Gorillapod's flexibility and grip is the construction of its legs, which are made from linked chains of nine ball-and-socket joints. The joints are individually very stiff and difficult to bend, but the leg as a whole is extremely flexible and can be bent into any shape quite easily. Each link has a thick rubber ring around it, so when the leg is bent around an object it grips with multiple points of high-friction contact. With three legs wrapped around an appropriately sized object the grip is surprisingly firm.
/bde613|48d0_10577-origbottle.jpg
Obviously with such a complex structure the main concern is going to be durability, since each leg has at least nine possible failure points; however I've put a Gorillapod Original through several months of fairly vigorous use while testing compact cameras, and I can report that it's showing no signs of wear and still grips just as securely as ever. I've also used the Focus for a couple of weeks, and so far it seems to be even less likely to break.
/7a1672|0bdc_10577-tree1.jpg
The Gorillapod Original and Gorillapod SLR have two extra links above where the legs meet to provide a bit of extra flexibility, and give the option of positioning the camera horizontally while gripping vertical objects. They also both have quick-release camera platforms. The SLR-ZOOM and Focus sacrifice both the extra links and the quick-release platform in favour of greater strength, with the legs attached directly to the camera platform. However the Focus does come with an adapter converting its standard ¼-inch tripod fitting screw to the larger 3/8th-inch screw used to attach professional tripod heads, so you can use it with your favourite head for extra flexibility.
/d8b748|8c7c_10577-tree2.jpg
There are a number of accessories available for the Gorillapod range, including spare quick-release platforms for the Original and SLR models, and some vicious-looking spiked feet for the SLR-ZOOM. All Gorillapod models and most of the accessories are available in either conventional plastic blister packs, or in eco-friendly recyclable cardboard packaging for a few pounds less, which is a nice idea.

Verdict
The Gorillapod is an ingenious and highly effective lightweight alternative to a full-size tripod. All the models are exceptionally well made, highly portable and offer an exceptionally versatile means of supporting a camera in a wide variety of situations. They are a bit on the expensive side, but are well worth the money.