This item I bought 2 months ago.
I work for a shop that sells these too.
The green 'gel' uses quantum force, same as the gecko lizard, to hold onto things. I found it left no residue at first and was very strongly sticky when attached to ridged plastic. It's no good on flexible silicone skins. But this is normal.
After a few weeks I noticed that dust, pollen, etc. settling on the green caused the material to become far less sticky so I submerged the end into luke-warm water with a touch of washing up liquid for a while. Dried it off and it was back to normal.
But after a period of sunny weather, I began to notice that pulling it off my phone seems to need more force. It is also leaving a fine sticky residue on the back of my phone.
I suspect this may be due to bacteria film perhaps growing on the green or perhaps a reaction to the sun?
I've asked Clingo for an explanation and am waiting for an answer.
I also had one customer in the shop returning a Clingo due to the same heavy residue left on the back of his phone.
Mine isn't that bad and I think a touch of citrus sticky stuff remover liquid will remove it safely (it did!).
UPDATE: Sept 2012
Regarding the sticky mess. I contacted Clingo and was told about and sent a new replacement pad free of charge.
The new item is a touch less sticky when warm and doesn't leave a residue.
The item surface looks far more transparent and so less intense green at the edges.
Works great now!
See image of the new one below.