I've put in a request to have this little beauty added to the product list, it appears to no avail.

I was always sick of stopping and lowering my seat for downhills. The Gravity dropper is an adjustable height seatpost you can raise or lower on the fly. This is brilliant. I click a trigger on my handle bars and can drop my seat by 1 inch or 4 inches.
Santa Cruz were offering this post as an option on builds when I was in the US last year.
I've had it a year and although it adds a little weight, it more than makes up for it as my seat is always at the height I want. I love it.
I've found this place in Essex that does them Riverside Cycle Centre
and their customer service is excellent.
For more detailed info checkout the Gravity Dropper Website.

my boyfriend has just ordered one of these, hasn't arrived yet but he has been wanting it for ever... i might have to borrow it and have a go i think

Ah I want to buy one of these for my other half for his birthday, but didn't know where to get it, thanks Queenie!

Just like to correct my comment on the customer service for Riverside. I needed a new clamp for the handle bar switch and I was so impressed when they promised to send me one free I posted this thread.

That was nearly two weeks ago. I spent three days at Glentress without my gravity dropper and really missed it.

After waiting a week I contacted Gravity Dropper in the US by email. Two clamps arrived in the post today from America. Looking at the prices on the website it's cheaper to buy direct from the US even with shipping and they do a new turbo dropper which looks good.

TBF Riverside's customer service may be better if you buy directly from them.

I have the alternative which is a Maverick Speedball and that is really good too. They now do one with a remote at about £170, luckily mine was a xmas pressie so I didn't feel the financial pain directly...