I know bitcoind uses the rpc, is there any way to query the bitcoind client to spit out a current number of addresses in use without using linux? Any cool blockchain querying windows applications?
Windows? Didn't that die yet?
You can get a Fermi estimate using bitcoind.
RPC command 'gettxoutsetinfo' reports 12.6 million transaction outputs.
That's an upper bound. Not all outputs are pay to pubkey hash, and some people practice address reuse.