Whenever you create a new partition in disk druid, it requires that you have a mount point for it. I agree that it should warn you when you forget to put a mount point, but there should be an option to tell disk druid that you know what you're doing. There are a variety of reasons to have partitions that you don't want to mount (including suspend-2-disk partitions), so creating a mount point for them just means you have to go back later, edit /etc/fstab and do an rmdir, which is annoying. (on the positive side though, the current scheme does give me an excuse to come up with interesting mount points such as /jeremyisacrackmonkey)
I've been thinking about changing this behavior...
You can also leave free space on the disk by using the partition by cylinder mode. Just double click on a "Free Space" region and create the partitions you require which have mount points. Leave space for the special partitions, and go back with parted and create them.