We are limited, went limited after 12 months of trading. It suited us as it fitted in with where we wanted the business to get to. We employ 10 fulltime staff and are about to add some more. The benefit was lower tax rates (corporation tax will be going up quite considerably soon though}. Limited liability reduces personal exposure to debt (provided directors guarantees arent given) and business finances arent intertwined with personal.
Administration is more expensive, there are higher accountancy fees and year end accounts need to be prepared by a chartered accountant and cost approx £2500 and upwards. Your accounts are available to anyone who wishes to see them so your financial position is more transparent albeit abbreviated.
I would talk to a couple of chartered accountants for their opinion on your particular circumstances depending on how you run or intend to run your business .