I know this is an old question, but it comes up fairly high in results of a Google search on this subject, so I would like to offer a more complete set of circumstances on why you might want either configuration:
For those who want to have two connections to two switches in case of any type of failure of network equipment to have full redundancy (like me) use two ports across two NICs on the host in active/standby connection to two separate switches. If you have a cable, switch, or NIC failure, you would still have access to your host.
For those who want higher performance through an active/active link aggregation, use two ports either on two separate NICs or on the same NIC to the same Cisco switch and have the ports on the Cisco switch set up for a port channel config BEFORE you configure the connection on the host. This is complicated, and only works with Cisco switches. Do not use this unless you are either working with a Cisco certified network admin from the very beginning of planning or ARE a Cisco certified network admin and have the whole thing planned out before starting.
In either case, this is connecting a switch to two ports on a network, If you take a physical switch and connect to two ports on a network, it will cause problems, not any increased performance, unless you have certain link aggregation configuration in place.
Use Active/standby for redundancy. Preferably, go through two NICs and two switches for full redundancy.
Use active/active for performance, but make sure to work with your network admin from the beginning. Do NOT use active/active for redundancy.