I like Hobbit/Xymon too. I had it running for about 8 years quite happily on an old DL380, single 733MHz cpu, 512Mb memory. I think the peak traffic it took was about 3500 status messages for 500 hosts. Almost all the messages were generated by scripts running on the server, grabbing web pages from all those hosts.

every business with a Web presence will have to incorporate 50+ different tax rules based on customer location

This has come up before, with Internet-based catalog sales. IIRC, there's more like 7,200 different tax rules to apply. Certainly around here there are different city tax rates in the nearby cities. My wife is looking into starting a small store, and as we're outside the city limits she would only have to calculate the state sales tax and not state+city sales tax.