Weight certainly comes into it, the bigger kites, 6' - 2m can drag someone off their feet. I've watched a biggish bloke on a kiteboard getting a couple of metres off the ground in a stiff wind above Westbury White Horse, while his mate was sporting some very elegant external steelwork with screws holding his shattered arm together after a gust suddenly dragged him off his feet as he was about to dismount his board.

but know nothing about them

Sincerely, find someone who does/ pay for lessons.

Compare, "Im thinking of getting a car for a bit of fun but know nothing about them,"

Just start small and work your way up. It's never hard to sell them on. Keep it under 4m and take it out in lower winds first until you get an idea of what it can do?
Also begin on an empty beach.
Have fun but be aware, get a gust and it might surprise you just how powerful they can be.

I think mine is 5 or 6 feet wide. In anything more than a fairly gentle breeze it is either terrifying, or embarrassing. There are few experiences to match that of being dragged a few hundred metres along a beach in full view of sunny day day trippers, while trying to keep your glasses on your face, your face out of the sand, and your trousers round your waist. Followed by standing up and attempting to run towards the (threatening to take off again) kite while also emptying a few kilos of sand out of your knickers.

It is much harder than people in the park made it look.

Use kite killers. Just let go of the handles and it'll come down like a bag of washing.

What cougar said...will save you a lot of hassle.

i have a 3m power kite - came in a kit (probably similar to [url= http://www.kiteworld.co.uk/acatalog/HQ_Beamer_Scout_3m_Power_Kite.html ]this[/url].

Great fun on the beaches of Norfolk. It's hard work, and anything over 15mph is very hard. I'm 12 stone, and get dragged down the beach on a regular basis. Sometimes face down with no control.

They're dangerous to kids walking underneath if you're not careful

There's a big kiteboarding scene in Hunstanton though; if you're nearby have a few lessons.