The ArcGIS Services Explorer is going to be a great tool to learn what is available out there. I had quite a few ArcIMS developers say that they can finally feel comfortable working with ArcGIS Server. The .NET and Java Web ADFs were too much for them and they were usually used to working with simple HTML pages. Compare the speed of JSON vs the speed of sending XML (AXL) requests to the server and see how fast you get a response. It really does highlight why the community at large has really moved to JSON.