In general, beer fests in the two countries take very different approaches to how beer is paid for and served.
Like twins separated at birth, American and British cultures can be both strikingly similar and surprisingly different. This holds true for beer as well. For example, much of the U.S.'s modern craft beer culture is built on styles traditional to the U.K.—like the India pale ale, craft beer's de facto signature style, which is originally British. Yet interestingly enough, American IPAs have become so unique, they've started to influence the way the style is made back on the other side of the Atlantic. The same goes for beer festivals: Both countries love them. And yet, many fundamental differences still exist.
As an American, I've grown accustomed to most beer festivals operating like this: You spend a large amount of money up front—somewhere in the neighborhood of $40 to $60 or more. For this price, all your drinking is taken care of: When you show up, you get a small souvenir glass which you take station-to-station. At each stop, you get only a small sample, but you can continue to get as many samples as you like throughout the session, which usually lasts about four hours or so.
British beer festivals, on the other hand, usually take a different approach: Any entrance fee is relatively nominal. Instead, you put down a small deposit for what is often a full pint glass that also has markings for third- and half-pints, then you purchase tokens (essentially paper money intended to prevent volunteers from having to handle cash) which are used at different stations to purchase beer by the third, half or full pint. As a result, you only pay for what you drink.
Both styles of festival have pros and cons, and frankly, much of it depends on what you are looking for. When I first started attending British fests, I often found myself frustrated. I wanted to try a lot of beers, but being forced to buy by at least the third meant that sampling 12 beers was the equivalent of drinking four pints (and keep in mind, British pints are four ounces bigger than American pints!) Granted, most festival workers would happily serve you tiny samples if you truly wanted to try before you buy, but the American concept of simply sampling a lot of beers with reckless abandon can be frowned upon. Instead, sometimes I would find myself buying a third and then dumping a bit which felt like a waste (of beer and money!).
But another major difference tends to stand out at British beer festivals: People don't get as drunk. Sure, we could chalk that up to a cultural phenomenon, but the way these fests operate actually present a very compelling explanation: American beer festivals are essentially drinking races. You pay an amount; you have a set amount of time: now go get your money's worth. Sure, most attendees probably don't purposefully think that way, but when you pay a lot up front, you inherently feel a subconscious pressure to make the investment worth your while. Also, because of the a set price, American beer festivals tend to be broken down into shorter sessions of just four hours or so to make sure the economics of the event work out. Meanwhile, a British pay-as-you-go festival can go all day—which gives you more time to do what you're intended to do while drinking beer… relax.
Needless to say, both these depictions of British and American festivals are generalizations. You can find examples of events run opposite ways on opposite shores (or in completely different manners all together). But much as the IPA has grown stronger by both countries accepting the other's innovations, it'd be interesting to see U.S. and U.K. beer fests take some lessons from each other.
Would it be so hard for American festivals to create some sort of tiered token system that still allowed patrons to pay up front, but that would stagger the prices to let people pay for whatever level of drinking they were actually interested in? Something like 20 chips for $20 and 50 chips for $40, with each chip being worth one sample? Meanwhile, it'd be wonderful if more British fests could understand the frustration of having hundreds of beers in front of you but being told you should try them six-plus ounces at a time. Surely offering some sort of set sampling fee with its own distinction should be possible.
Still, possibly the best difference between American and British beer fests is that they're different in the first place. Both countries' beer cultures were forged out of the fight against homogenization: In America, that was the fight of craft beers against big beers; in the U.K., that was the fight of "real ales" against mediocre lagers. Though both styles of beer fest have their pros and cons, homogenizing the cultural differences would also defeat the point. That said, a wee bit of improvement never hurt anyone.