Most of the 1,200 UK outlets of the fast-food giant will serve up free Wi-Fi by year's end: The Cloud will handle the build-out, apparently, although that detail is mentioned only in passing. Hotspot service costs around £5 ($10) per hour in England, so this might have an impact on pricing and users. Jiwire lists nearly 24,000 hotspots in the UK.
In the US, about 9,000 of 12,000 McDonald's locations have Wi-Fi, operated by Wayport, which is a paid offering. While I sometimes read that McDonald's offers free access with a purchase, that doesn't appear as a policy, nor is it stated anywhere in information McDonald's makes available about its Wi-Fi. Free service is, however, provided to Nintendo DS users, an instant-messaging appliance's users (Zipit, starting in mid-Nov.), and subscribers to AT&T WiFi Basic.