At the same time as the applet was in active use, we built (credit for the good parts goes to Joe Sirott) a server-side map that required two clicks to mark a rectangle. Joe's implementation had a nice Active X interactive selection, but again we could not use it on a enough browsers to deploy it. Joe has since built other nice map widgets. I built the "two-click" version. It worked. On all browsers, but as one user put it so eloquently: "It's not draggable, dude".
Next up was a long experiment with Google Maps. I built a widget that allowed click, hold and drag drawing of rectangles, horizontal and vertical lines using markers on the corners and mid-points. It worked. Sort of. I could get it to work fine, but I was slow and patient. When users used it the response was so sluggish they the were immediately frustrated. Another killer was the projection. We deal mostly in global data on a rectangular equal-area projection. The Google maps modified Mercator looked terrible on the global view and the selection scaling when dragging a rectangle above 60 north was dramatic and disconcerting.
Enter OpenLayers, the GWT-OpenLayers project and a client that said rightly that the Google Maps implementation was s!@$. I built yet another map widget. I think it works well. Editing the selection is not as slick as was with the Java applet and the strict modal interface is not ideal, but I haven't heard of any browser compatibility issues. And eliminating those was the goal all along.
No doubt this would be more interesting (slightly less boring?) if I had links to all the previous map implementations, but it seems like too much to figure out how to find or deploy stable examples of each.