Review our idea: ip-address tracker for web-developers

While working on some of our projects we've been struggling the problem of preventing spammers or trolls from posting. Unfortunately, captcha is not always a solution (like for example when you have a vote widget, you wouldn't want your users to enter captcha). Browser cookies are not effective, of course. So, you have to track ip-addresses and make sure one ip does not send, say, more than 10 requests to a particular action during 15 minutes. Of course the primitive implementation is a 10-minute session of unintellegent coding. But over time things get more sophisticated, especially when you need to add new rules, track browser user-agents and assign each ip a trustworthy level. So out of 10-minute boredom code it grew into something slightly bigger.

Now we've been thinking. Would anyone be interested, if we make a webservice out of it, a lot like ReCaptcha: with an API and, say, libs for some popular languages, so that anyone could collect, manipulate and validate ip-addresses in their web-project. It would work like this (the simplest case):

1. You send a check request with an ip_address of your user to our service using our API. 2. We check if this ip exists in our db, if no - we add it. 3. Check when was the last activity from it, then check the rules that you set up in our web-interface when you signed up. 4. Then send you back true/false answer based on the rules and on this ip's previously stored data. 5. Based on this simple answer your application decides what to do with the user (so, it would take a 1 line of code to set this thing up in your app).

The service would also provide warnings (email, probably sms) about blacklisted IPs and a web-interface to manage IPs.

What features would you pay for? Or would you at least use it for free?