MachineInstr and Machine/BasicBlock Metadata

Has anyone done any work on adding Metadata to MachineBasicBlocks, BasicBlocks or MachineInstrs? I have seen a proposal here(for BasicBlocks):

http://lists.cs.uiuc.edu/pipermail/llvmdev/2010-April/031233.html

and wanted to know if anyone knows anything of this or would be interested in using it if it was done. Thanks

Andrew Stanford-Jason