Use node for anything that has a HTML(5) front end. The big win is that you no cognitive disconnect between the client-side and server-side code. The productivity increase is significant.
All the async event goodness (which is great for streaming of course) is just icing on the cake.
The biggest advantage I see from my experience with node.js is that you can code in just one language from the client side to server side. Of course, server side JavaScript is _not_ exactly the same as in client side - but for most part, that does not get in the way and the language basics remain the same.
It also helps that it scales well for the traditional web apps, and currently there is a huge momentum behind it, and an active community working on it.
The site reads and writes to last.fm in the background and pushes updates to client's browsers while doing so.
I'm sure it would have been possible to write it using some other technology but node.js just made it so easy. Also, writing the entirety of the app in just one language was an additional bonus.
I'm excited about building something bigger with it soon.
Is this alternative client for last.fm? I wonder how useful developing alternative clients can be apart from learning purposes. I have seen a lot of twitter clients coming up. Do users really care about using these?
To some extent. It copies a user's scrobbles/now playing info to one or more other users' profiles. So if a bunch of you are in the same room listening to music you can all scrobble at the same time.
That said, it was mainly written to get to grips with node. As well as to scratch a personal itch, obviously.
The great thing about node.js is the flexibility it provides. It isn't what Rails is to Ruby or Django is to Python, really it is a way for Javascript to interact with the OS outside of the browser, e.g. on servers. This versatility leads to a ton of options, which many don't even focus on the web. With that in mind, know that using node.js is more than building a web app, it has given us slick tools to do things that in other languages or options would be painful or annoying.
I personally have made simple tools with it, like a desktop image uploader, or a cli gist (github) maker. I enjoy how easy it is to connect many different technologies together with very little effort.
"A browser based real-time multiuser sketchpad" - It made me think if it is possible to develop a collaborative, online, vector graphics design tool. Not a heavy application like Illustrator but something like light version of InkScape that can help in quick and easy graphic design for web such as logos, buttons etc.
It runs queries against a pool of lookup servers and aggregates/returns the results in real time. I'm also using it as a fast, low footprint HTTP server.
https://github.com/dandean/express-form and https://github.com/caolan/forms are two good options. Out-of-the-box validation for model-based forms is a little bit trickier — there are many persistence options and each has their own way of doing things, which isn't always model-based.
(Although the hosted version is currently in closed alpha, you can check out progress on GitHub.)
If you want something more Tweetie than TweetDeck, check out Streamie: http://streamie.org/