I think the reason so few people use it is because, years after the first release, it's still so complicated to set up.
I did configure Bitcoin Core to run that RPC server, here's bitcoin.conf:
server=1
rpcuser='me'
rpcpassword='youwish'
Then tried to run run_p2pool.exe, but could find no option to configure the rpcuser there. And of course it failed.
In the log I noticed:
Testing bitcoind RPC connection to 'http://127.0.0.1:8332/' with username ''
So I went back and set rpcuser='' in bitcoin.conf
And I ran p2pool again this way:
run_p2pool.exe -a myrichwalletiwish youwish
And still it didn't work. So I went back to a normal pool, because I have other things to do today.........
