router lifetime

[Franck Martin <franck () genius com>]

How long do you keep a router in production? 

What is your cycle for replacement of equipment? 

For a PC, you usually depreciate it over 3 years, and can make it last 5 years, but then you are stretching the 
functionality, especially if you upgrade the OS, tho it is not uncommon to see companies still on XP and IE6. 

I'm wondering what is the rule of thumb for routing hardware? Same shelf life as a PC or you keep the hardware much 
longer?