I did spec a couple of 7m dacs a few months ago to run between two adjacent bays, but normally for more than 2m I'll just drop a SM sfp and run a preterminated fibre cable.

In the field its the armoured fibre on a reel, 100m, 200m, 500m etc, with opticon connectors, or some normal cat5 typically for APs

Some network guys I know prefer fibre even within the rack, just because they don't want the weight and the obstructions in the rack. Apparently more than once the weight of the DACs and the bulk of the cable bundle has caused a problem with NICs.

Personally that surprised me, but I can see where they're coming from.