Here in arguably the most mobile-crazy country in Europe (I /think/ we've overtaken the Finns in mobile-mania), there's a clear split between those on a contract (like me) and those on pay-as-you-talk schemes. Basically, if you can't get a contract because you can't afford it, are a bad credit risk, don't have a direct-debit capable bank account, or whatever, you go pay-as-you-talk.
People like me who can't be fussed with faffing about with vouchers and such, and like a new free phone every year, that's insured lest I drop it in my beer, go contract.
One thing's for sure - the mobile companies want people OFF the pay-as-you-talk regimes. The prices for those are going steadily up (I think the cost of an SMS message is now about 15p on PAYT versus 3p for me on my Orange contract), because pay-as-you-talk is quite simply not compatible with always-on arrangements like GPRS and G3.
In short, the riffraff have PAYT, whilst us professionals :) have contracts.