Read on, and find out what technologies I'm referring to.
The Platform Is Ready
Integration Opportunities Abound
Integration comes in two flavors. First, you might want to use data from other sources, like Google, Facebook, and Twitter. Second, your idea may not be suitable for an entire Web application, and might fare better on the desktop, or as a widget. There are great news coming from both fronts.
JSONP is an easy way to get data, despite the cross-domain restriction policy, and major companies have been taking it seriously. Google's search API and Twitter's API have JSONP support. Yahoo's Query Language goes one step further and lets you get other sites' content wrapped up in nice JSONP. Did I mention Dojo's seamless support for Google's search API?
If you want to integrate your application with your user's desktop, you have Google Gears and Mozilla Prism today, and HTML5 in the future.
Applications that don't need a lot of screen space can be packged effectively as widgets. Widgets are supported natively in Mac OS by Dashboard, and in Vista's Sidebar. For a more cross-platform solution, you should check out Google Gadgets, which work the same on the Web, in the Mac OS dashboard , in Linux, and in Windows.
Oh, and one more thing. Google's gadgets also work in their productivity suite - in Gmail, in Spreadsheets, and in Google Sites. So you could impress your boss by building a dashboard with important numbers straight into their Gmail.
REST Decouples Client From Server
Remember ugly long URLs? REST (Representational State Transfer) is a collection of design principles which yields the opposite of those long URLs. It matters because, once your client-server API obeys REST, your client is not dependent on your server implementation.
Using REST designs with JSON input and output gives you "standardized" servers that are easy to interact with, and easy to code. On the client side, for example, Dojo automates the data exchange for you. On the server side, Rails scaffolds have built-in REST/JSON support, or you can pick up ready-made App Engine code.
Hosting Can Be Free
Web applications are very easy to access, but the servers are a pain to setup. Furthermore, hosting costs money - even if you're on Amazon EC2, there's a non-zero amount of money that you have to pay. Most of us, programmers, don't like to pay for stuff.
Fortunately, there's the Google App Engine, and it has a free tier which is pretty much equivalent to running your own server. "Pretty much" covers everything except storage, which is currently capped at 1Gb.
If you prefer gems to snakes, like me, check out Heroku for Rails hosting. Heroku's beta platform is free, and they promised a free tier on their production version. Their free tier may not end up to be as generous as Google's, but you can always downgrade to Python if your application becomes successful. Update: Google's App Engine can run Java now, which leads to support for Ruby and other languages. This post has more details.
Thanks for reading this far, and I hope you have found this post to be helpful!