Unlimited is defined by some dictionaries using the following words: not limited; unrestricted; boundless; infinite. What these dictionary writers are getting at is that something unlimited cannot have any limits. The clue is in the word. So why are we surrounded by companies who don't seem capable of walking to their nearest dictionary and looking up a word?
To pluck one example out of the clear blue sky (ahem), the iPhone launched this week in the UK. One of the selling points is the 'unlimited' data plan you get with it -- but it isn't unlimited at all. What your £35 a month buys you is a monthly limit of 200MB. Okay, you could possibly argue 200MB is a generous limit, but unlimited doesn't mean generous. I'd say that 200MB, being a limit, is the opposite of unlimited.
The same fundamental ignorance about what unlimited means exists with some Internet service provides too. There are a number of them who call their service unlimited, then proceed to limit the service using a 'fair usage policy', or FUP. A FUP means, while you can technically download whatever you want, after you hit an often unspecified limit, your ISP will make it harder for you to carry on, either by slowing your connection down, or just cutting you off totally.
I'd like to rant about this more, but my unlimited* column inches are rapidly running out, so I'll end by saying that if you want to use the word unlimited, at least look it up first.
*Fair usage policy applies, first 300 words are free, every word after that costs £1 in donations to the office cake and beer fund. Terms and conditions apply, see press for details, does not affect your statutory rights.