I just read a very interesting blog item on The Healthcare IT Guy, Guest Article: Rich Internet Applications for Improved Healthcare App User Experience . Since I have spent time on this issue, especially as it relates to Microsoft's Smart Client Platform, I thought I'd add my own 2 cents:
Thin vs Thick clients is always a great discussion. Microsoft has the "Smart Client" platform which is essentially a thick client UI that uses web services on the back-end to connect with the data-store. This has the benefit of allowing the "Smart Client" application to work in distributed environment, just like a typical web application.
The "rich" windows UI of the Smart Client is the advantage over a web UI. Ajax however is making web applications look more like a rich Windows-like UI. Just check out, for example, the new Yahoo mail (my personal email platform).
The Smart client distinguishes itself by allowing for an "off-line" mode, which is great in scenarios where Internet access is not always available. Installation and deployment however is the downside of the Smart Client, although it has been made easier with this platform. This is where pure web applications shine.
I wonder if Microsoft is still committed to the Smart Client now that they have another UI platform in the works, code name "Silver-Light", which will further bridge the gap between a Windows and Web UI. We'll have to just wait to see how things sort out in the end.