In a dormitory of 550 residents, people often mistakenly set up DHCP servers for the whole network by plugging in their private Wi-Fi routers wrongly. Also recently, someone mistakenly configured their PC to a static IP being the same as that of the default gateway. We use cheap 3Com switches at the moment.
I know that more advanced switches support DHCP snooping to solve the DHCP problem, but that still does not solve the default gateway IP takeover problem.
What sort of switch equipment do real ISP's use so their customers cannot break the network for the other customers?
Edit: What we ended up doing
In case anyone are courious, we ended up doing seperate VLANs for each user. And as a matter of fact, not just the 550 users, but for 2500 users (11 dorms). Here's a page describing the setup:
http://k-net.dk/technicalsetup/ (the section "Transparent firewall using VLANs").
There was no significant load on the router server as I feared in one of the comments below. Even at 800Mpbs.