Connecting two routers together is fine if they need to. If routers were never connected together, the internet would not exist.
In Yahoo's case, it depends on how many networks (networks meaning a group of hosts under a single broadcast domain) they have and the number of ports available on the routers etc...
Using a crossover to directly connect the routers together works and is simple. You can also use dce/dte cables on the serial ports as well which would save you using an ethernet port.
If your router has an auxiliary user interface (AUI) port you can get different transeivers, I believe, which you could use to connect them together.
You can also connect them if you have WICs installed (Wan Interface Cards) but these are made for WAN connectivity obviously."Secondly the console port is the only port on the router that allows an engineer to configure the IOS of the router."
You can also configure cisco routers to accept incoming telnet sessions. (line vty ...) which allows remote administration.
I think the main reason for the console port is security. If anyone could simply access the IOS through any interface, it would leave the router open to a lot of intrusion attempts. Regardless always password protect your routers.
As mentioned above you can use the serial interface to connect directly to another router, or else you can use it for WAN access too, such as frame-relay.
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