in reply to web-based application or desktop application?
I worked on a web-based project in 2000 which I considered to be very complex. It took myself and a fellow programmer almost a year to get the thing right, but when we did... it was easy to maintain and update. The complexity of the interface involved being able to drill into and back out of some 21 million records spread across 400 databases (MySql) each containing about 15 tables. The basic premise of the app was that business machine cost/performance could be tracked nationwide across all makes/models of machines (mostly copiers). By the time we were done, a user could drill into a particular machine, sold my a given office and maintained by particular technician and find out cost/copy, overall maintenance cost/hour/part/copy etc... .
The application is the core service of the company we were coding for, and they are very successfull with it. My point here is that it was a long hard grind to make that UI work, but it did pay off. A distibuted client app would have never worked... .
We did (often late at night, with very red eyes) question the feasability of the web approach, and it was worth while spending the time questioning it. But I would venture to say that the company we wrote the code for would be out of business had we tried anything but the web app approach.
Just some encouragement... :-)