I set up a surveillance system for an employer once, and never wish to do so again: I hate fiber glass insulation, and it hates me. One of the coolest things about it, at the time, was the fact that it came with a webserver, so you could patch in and see what was going on.
Archerfish takes this approach to its brainstorm-session extreme, with alerts via SMS, email, "personal Archerfish portal" and various other net-aware extras. Its motion-detection system is fine-tunable, it can discern people from other objects, and it automatically organizes "events" it observes to make review fast and easy.
At $2,500 for a 2-camera, standard-def system, however, that commercial-grade villain-recognizing software doesn't come cheap -- especially considering that it also has a $20 monthly "service fee" to maintain access to the the web-based features.