Oh, I have. During "routine traffic", found data to be only 10KB/s much of the time... on eSignal, tracking about 200 issues in real-time. (Not a typo... "KB/s".) Dialup is easily capable of handling trading/data requirements for most ETers. Another alternative is just to be able to call the trade desk if your internet connection goes down and you don't want to hold until it comes back up.
Excellent advice. Regular retail routers with dual WAN inputs don't instantly switch connections. 30-45 seconds is being nice. It could take even longer. In my home, my primary is Time Warner Cable. I also have Verizon DSL as backup (and the DSL also runs my VOIP phones). When my cable goes down, I switch to DSL using wifi.
If you are manually entering orders a few times a day, I might suggest a different solution than if you are running an automated trading system on higher frequency data. In any case, as you research options you may want to review this thread I started last year on the topic of dual-WAN routers: http://www.elitetrader.com/vb/showthread.php?s=&threadid=226178