Hey,
This is more of a vCenter question, and you posted in the vCloud Forum. Alternatively, if you have support, you can create a support request for more assistance.
For vCenter 5.1, I think the limit should be 128 Distributed Switches ... see: http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf
vCenter 4.1 & 5.0 = 32 = http://www.vmware.com/pdf/vsphere5/r50/vsphere-50-configuration-maximums.pdf &http://www.vmware.com/pdf/vsphere4/r41/vsp_41_config_max.pdf
vCenter 4.0 = 16 = http://www.vmware.com/pdf/vsphere4/r40/vsp_40_config_max.pdf