Before I point you to the merits of the Eclipse RCP I'll just digress for a moment and say Happy New Year to all those who deem the new year to be on first of January. I hope 2006 brings many epiphanies for you.
But like I was saying, the RCP is a stunning platform to develop on top of. Every piece of your application is packaged as a plugin so modularising your app is simple. On top of that, you get advanced update and management capability out of the box.
If you need a quick demonstration of its power, then take a look at EclipseZone - Why You Should Use Eclipse RCP (In 10 Minutes).
It'll prove to you the merits of developing on the eclipse RCP platform better than any words could.
btw, the link embeds a short movie clip to walk you through the process of creating a RCP app with eclipse. Unfortunately, it does not work in firefox. However, there is a plugin which with one click allows you to open a site in IE. It changes the current tab to an IE tab. Seemless IE integration! A very useful ie plugin.