One of more intriguing reasons to use UMN MapServer is Ka Map. I’m quite impressed with how it is able to pan and zoom without having to load the whole page. We’ve tried to do as much as we can on the client side of ArcIMS and with Ka Map we can continue that trend.
Since ESRI released ArcIMS 3 a couple years ago, there haven’t been any big changes to the default templates. I’d love to see ESRI offer some new ones on their site for those who can’t hire someone to customize ArcIMS for them or have the to do it themselves. Maybe with the advent of ESRI Developer Network and the Code Exchange we’ll see some more, but I doubt it.