Well, many people will be surprised to hear that Akismet is now charging for accessing its anti-spam database. Lots of users will disagree with the way Akismet handled this too. Bundled with WordPress, all you had to do was create a free account to get your API key. This worked across multiple sites and was pretty seamless.
Now a charge (currently $50) is levied for businesses and affiliate sites. Furthermore the free accounts are throttled with traffic priority going to paid-up subscribers. This from their website:
If your site is for a business, or if it promotes a product or service, you should pick from one of our paid account options.
Hmm, create a free tool, get subscribers then levy a charge. Whatever way you look at this, it’s going to be big business for Akismet with hundreds of thousands of people ready to subscribe.