I have a version of WinUAE kaillera but have never found anyone to play with. Unfortunately I'm afraid it won't work too well anyway since Amiga emulation doesn't runn all too well on all machines. This means that you might get some serious desyncing if one computer is lagging just a bit. Then there's the fact that everything must be identical. Same rom, same config, same ADF file. This is of course to increase compatibility but I'm afraid it'll be much too hard to find people with the exact same setups.
And there's still the problem of compatibility. I haven't seen a newer version of it in a while, and the one I have I'm afraid won't log on to any server any longer because it's outdated.