The ARRL has an interesting bit about interference being caused by a wireless network installed in an apartment complex. This is due to the fact that current 2.4Ghz wireless networking gear operates under Part 15, allowing devices to be used in a given band as long as they don't cause interference to licensed users. The FCC has sent a "Notice of Inquiry" to the company that installed the system. This is most likely going to be a very big problem moving forward as wireless networks become more ubiquitous, spectrum is scarce and as most people know, cohabitation of wireless networks and other spectrum users is not at all like running two pairs of Cat 5 next to each other. Read more here.