The default configuration when adding multiple uplinks to a vSwitch "Route based on originating port ID" which means the different VM's are connected to the uplinks in round-robin. This configuration allows you to connect the uplinks to different switches without the need of special configurations on the physical switches, since only 1 uplink per virtual machine (MAC) is active at any one time.If you have multiple uplinks, all active. Once one uplink fails, ESXi will immediately fail over the VM to another active uplink. So basically it will load balance between these 2 uplinks.
Lets say you have 2 10G uplinks in active/backup -> effective bandwidth is 10G
Lets say you have 2 10G uplinks in active/active w/t LACP configured from s/w side -> effective bandwidth is 20G
"Route based on originating port ID" you can use active-active without doing any extra additional configuration from the Physical switch side
You can also refer below documents
http://www.vmware.com/files/pdf/virtual_networking_concepts.pdf
http://kb.vmware.com/kb/1022590