but as I understand it you can't just sell them/transfer them to cash... you have to put them up for sale and then someone has to buy them ?
An associated risk, you
can sell in a falling market but as you would imagine you may have to put your 'ask' slightly lower than the dip to get it bought up quickly.
Naturally the more coins you have the more difficult it becomes to 'get rid' in a hurry, if you had say 100BTC and the market started to fall at £3, there may be lots of little bids ranging between £2.80/£3.00, so some of your 100BTC would be sold at one price, some another, etc, depending on sizes of the other persons' bids.
I've put money in via intersango (best GBP market) and I could sell up now for a half decent profit, but I'm holding, if I see the market crap itself I can pull the trigger and get rid if needed.
What I would recommend anyone do is read into bitcoin and its potentials
http://www.thebitcointrader.com/2011/12/10-most-anticipated-bitcoin-projects.html one of the main pluses is you can open an
http://www.intersango.com account and put £1 into it and trade with if you wanted, it's not like buying stocks and shares where you need £X,000 to even get looked at.
*I have no ties or relations with intersango, it's merely the biggest GBP/BTC exchange.