Minor U-verse annoyance: their wifi is integrated into the cable modem and has a fixed SSID and passcode. They said I can't use my router.
So now I have to change the login settings on every one of my devices. PLUS the code is one that I'll never remember.
That's more than a minor annoyance!
That's when I plug in my own firewall. If you have an ethernet jack with dhcp a nat'ing firewall will work.