Hello Patrick,
In theory, one should mount the switches/routers in front (toward cold isle) of the rack to have an optimal airflow, but then cabling get a little bit messy.
If this type of equipment is mounted in the back (toward hot isle), the cabling can be done much cleaner, but the airflow isn't optimal and in worst case, switches and routes take in hot air from other devices.
the most elegant solution is to buy devices in a reverse airflow configuration. That is however not always possible. The worst type are switches with sideways airflow, since those will always suck up warm air. Those with regular airflow you can at least mount inverted into the racks (and get a cable mess, as you predicted).
we just got a bunch of cheap 10GE switches for a test platform, and these only came with a regular airflow configuration. The workaround here was to order them with fiber SFP+ instead of copper DAC cables, since fiber cables are much easier (because they're thinner) to route through half the rack.
whatever you do: set up polling of the inlet temperature with SNMP if your devices support such a MIB. ColoZH can get _very_ hot and it's vital you know whether you're slowly cooking your devices, or whether they're within specs.
Cheers, Markus