Timetric Makes Web Data Useful with Time Series Analysis
readwriteweb.com
readwriteweb.com
I admit to being biased, though; I know the founders and they're all really great and wicked smart guys. :)
There's also the API and the ability to build models which get updated when the underlying data's updated. Timetric is much more a time series database with visualization on the top than it's a visualization service which incidentally happens to be a data store.
If anyone out there needs a time series database backend for something they're building, get in touch with us: we'd love to talk with you.
I think the smarts comes in comparing multiple data sets, over time.
(I'm one of the team behind Timetric.)
We've not so much left it out as not got round to it yet! Counting the number of entries - is that what you're after? - is a nice idea: we were thinking more of a series of values a-la RSS-CB (http://www.cbwiki.net/wiki/index.php/RSS-CBMain), but it sounds like they'd both be good things to do.