Got some questions in inbox regarding tcp, udp and socket.io, so i'll just paste the response here, maybe someone will find it useful:
Yes, indeed it is using tcp for transport, and no, there is no indication that it will support udp (Some security issues with browsers, as it seems, there was some talk about it on socket.io mailing list).
I don't see that as a big issue, advantages of socket.io are multiple (main advantage is that you can use them in a browser, as for udp there's no client library or other possibility to get it in browser), and in my opinion, this is the best starting position to write a some sort of browser/node-webkit multiplayer game. UDP is something that is really useful and has some advantages (speed) but i believe it's something you should add in a "second stage" (whatever that means)of development, and build it with writing actual code - not inside construct 2.
Also, there's a "volatile" method in server-side of socket.io that behaves somewhat similar to udp (it won't get delivered if the client isn't ready to recieve it.) so that should help to speed things up if speed of websockets (?!) is an issue!
But why not, i'll try to make a simple udp plugin, if node-webkit supports it! (but not so soon!)
Also, on the side-note, this whole thing with writing a server in construct 2 is currently just an experiment, we must think "outside of the box" how to set-up whole "multiplayer" thing with node-webkit if we want to make some feasible solutions. It's not impossible, hell, last week i never really thought that it will be possible to write any kind of server in construct 2, and that changed, so who knows, we'll see what future brings!