Bandwidth is still a limited resource. Some say this will be for a short time only, as telco and cable companies will soon enlarge the available bandwidth. This, I believe, will not end the problem. But even if it does, you're not designing pages in 1999, you're doing it today, with the bandwidth we currently have. Don't just write applets, write them good.
Applets are just like any other program, and just like any other thing that zooms across the web.
Keeping them small is an art you can learn. Using .zip files or applet JARs minimizes the number of connections to be made, and helps speed download time. Beware of animated GIFs. If you do them, do them right. Use the proper tools and keep sizes small.