Looking at the newly available ASP.NET AJAX Control Toolkit, there are several things I really like about it.
- It has a quickstart with a sample page for each control.
- It takes less than 5 minutes to download and get running.
- The controls are mostly cross-browser compatible.
- It's free.
- It's open-source.
- It's practical - i.e. the controls are based on useful needs, not just flashy toys.
I especially like the ModalPopup and PopupControl. The first presents just that - a modal popup (which nicely fades out the screen). The second provides a dropdown-type control which is great for X-Pickers (Date-Pickers, Employee-Pickers, Color-Pickers, etc...)
Even if you're in an older shop that already developed a lot of your own controls, it's still worth investigating because these are (1) standardized, (2) likely to continually improve with the support of an entire community, and (3) potentially better and more robust than a control that a single dev whipped up a year ago under schedule pressure.
What I notice is that these controls abstract a lot of complicated DHTML features, like drag & drop, multi-layering, and DOM-modification, all while being cross-browser compliant. In a way, it's reduced advanced DHTML to mere copying and pasting.