Today I extended existing profile json API (https://mining.bitcoin.cz/accounts/profile/json/) with worker stats. Now you can monitor your workers in easy way: timestamp of their last submitted shares (unix timestamp in UTC), approx. hashrate (unfortunately for current round only, so it's not very exact for short rounds or slow workers) and if they are alive (currently fixed 3600 second threshold, will be possible to customize it soon).

I also see that some people are polling json api very frequently (some guys even many times per second!). Because data in json calls are cached for 60 seconds, you're doing 60x more requests than necessary . Please change your polling interval to something sane, otherwise I'll have to solve it somehow ]:->.