Listiti goes after the new Twitter lists by generating hourly alerts to you via email (currently they only offer hourly) on keywords found in that list. The idea is a bit more complex and complete than you think.
The idea of Twitter lists is not to follow the hundreds of people directly, but to follow a list of people to get information on a topic. Well if you are not following them, some of the other alerting systems won’t work the way you wish. You could do a general aslert based on everyone on Twitter, but then you get too much noise.
Listiti will watch keywords in specific lists that you specify. Narrowing the search and the group of people watched. They have a selection of top lists, or enter your own and the keyword you want watched. For example, watch a list of the social media ‘experts’ for a new product name mention.
They also have badges that can not only show what list is being watched, but as a promotional tool for that list. You can also unsubscribe from an alert at any time by clicking on the link in the bottom of the email you are sent.
Currently there is no charge for the service, yet the developer requests some free beer.