From a networking perspective, there is not too much difference between trunking and adding additional adapters in hardware.
With more adapters in a server it also becomes more complex to control routing.
A more preferrable method (at least in my opinion) is to assign the servers into relatively small VLANs. These VLANs can be set up for servers belonging to the same customer or (load)sharing the same application.
With smaller vlans you are able to use a single or teamed adapter for all traffic flows and you are still unlikely to run into network-load issues.
Regards,
Leo