Hmm, sounds challenging, but I think it can be done by using a slightly complex partitioning scheme.
You need separate partitions for root (one for each distro), and a common boot partition for the kernels, and home partition (your email and bookmarks will be under you main user).
You might also be able to have a common /usr partition for all the distros, if you are carful when installing the applications. If this doesn't work you might be able to put the larger server installations on a common /opt partition.
Others might have some experience on how to do this in more detail. Good luck.