That is still not new
The chess servers have been doing something similar to that (automatic notification of when people you are interested in show up) at least since the mid-90's.
I highly doubt that it was original even then.
Cheers,
Ben
"Career politicians are inherently untrustworthy; if it spends its life buzzing around the outhouse, it\ufffds probably a fly."
- [link|http://www.nationalinterest.org/issues/58/Mead.html|Walter Mead]