VMware released vCenter Converter 5.1 Beta to the general public last month and its available for download now from the VMware VMTN Community.
As I found with my recent vSphere 5.1 upgrades, vCenter Converter 5.0 is not fully compatible with vSphere 5.1 farms and there are a number of issues.  In my own experience, a conversion is extremely slow using Converter 5.0 on a vSphere 5.1 farm.  Other issues were much more serious.
vCenter Converter 5.1 Beta has a relatively short list of known issues (taken directly from the VMTN post) and the ones listed are reserved for Linux guests:
- You cannot upgrade an existing installation of Converter Standalone to Converter Standalone 5.1 Beta. Before you install Converter Standalone 5.1 Beta, uninstall any earlier versions of Converter Standalone and delete any remaining Converter Standalone server database files from your system.
- You cannot convert physical SLES 9 sources, if the root directory is located on an LVM disk. You need to convert the LVM disk to a basic disk.
- Virtual machines cloned from RHEL6 and SLES 11 sources have no network connectivity. After the conversion is complete, you need to reconfigure the network settings on the destination virtual machine manually.
- Virtual machines cloned from SLES 11 SP1 sources boot in console mode. After the conversion is complete, you need to recreate the xorg.conf file.
Download it now at VMTN:Â http://communities.vmware.com/community/vmtn/beta/converter_standalone51