http://green.itweek.co.uk/2007/01/used_network_ki.html

But can second hand bargains also work when businesses are looking to buy enterprise class network kit?

Well, there are plenty of firms out there who do successfully buy second hand network kit from enterprises or leasing companies. Some enterprises refresh their kit every three to five years and lease companies pick up the kit after the lease runs out so both can supply a steady stream of second hand equipment to the market.

Some critics would question the reliability of such aged machines, but remember, this kit has typically been sat in a nice, environmentally controlled datacentre, and if it had the right configuration programmed in when it was installed, then the only hands that might have touched it are those of a network technician just plugging in the requisite cables. After that, it’s remote management all the way.

An interesting article and very relevant.  Re-using hardware can make sense, particularly for the non-production environments, the only thing you’ve got to watch is the risk/cost ratio, the only thing to watch out for is the availability of parts/replacements and possibly their power utilization.