No, the only user-specific data that is sent to and from a pool and worker are the worker credentials (username / password). No hardware or PC info is sent.
The only way to guess who on a pool has an ASIC is to look for any 60GH/s workers coming online. If someone pops online tomorrow with 180GH/s, it would be assumed that they have 3 ASICs, as it would be damn expensive to do so otherwise.
Where can we find these kinds of stats? I am curious to know approximately how many ASICs are in the world mining right now, if any.
Most of the popular pools have some sort of statistics, rankings, or "hall of fame" type page that lists the top miners on that pool. There's no network-wide rankings page listing individual miners though.
And I believe most of Avalon batch 1 (300 units) are out, as well as 6 TH or so from ASICMINER.
For example, this page is the list of top miners at BTC Guild, currently the pool with the highest overall network hashrate:
http://www.btcguild.com/index.php?page=rankings
