Not all O2s fault
I don't think O2 can be blamed from calling their previous web packages 'unlimited'
Obviously most Reg readers would quickly notice the asterisk next to any unlimited package and read the entire T&C until they knew the exact limit.
If O2 had previously advertised it as a 200Mb limit most people would instinctively look for an "unlimited" package elsewhere, without even checking the true limit.
After all, its more logical to assume that a 200Mb limit is worse than an Unlimited* package, unless you're cynical.
I agree that nobody should use the term Unlimited unless it truely is. If I bought a Honda with an unlimited milage warranty thats exactly what I'd get!