A patent for redirecting browsers to a login page, regardless of settings, applied for in 1999, granted last October, means that pretty much any company running wireless hotspots will have to buy a license. See Wi-Fi Networking News: New License Fee May Face Operators.
I suspect that most hotspot operators will be liable for this as there’s only really one obvious way to do it (transparent proxies).
I’m not very keen on the recent habit of granting patents for things which are pretty much the only way of doing something, such as this. It’s not really an invention but a combination of prior existing technologies (NAT, proxies, AAA systems).
In fact, this one is so obvious that Neil and I came up with exactly the same idea at Trivanti in early 2001 with no knowledge of the patent. We didn’t end up going anywhere with it, due to reluctance of the company to enter into the hotspots business (and eventually , any business!)