If you don't have a seperate /home partition, you will loose them. Here's a strategy for multiboot or frequent re-installs:
Before doing anything, copy your personal files to an external storage medium (or a separate internal if you have).
Wipe your disk, then create a (primary) partition /data (or how you want to call it) for your personal data. For multiple users, create multiple /data partitions. Depending on your needs and disk size, I suggest 25% to 75% of the disk. You can dedicate the rest of the drive to an extended partition wherein you install your linux distros.
You only need one swap partition for a multiboot installation. So,
- create a swap partition as /dev/sda6 (about 1.5 times your RAM)
- create several (depending on the space) partitions for linux distros (if you want to multiboot), calculate about 10 to 15 GB per distro
- do not create (a) seperate /home partition(s)
Install linux to one of the "distro" partitions. For multi-boot, be aware of GRUB and GRUB2 issues if a *buntu is in the game.
On your /data partition, create folders for /documents, /downloads, /images, etc.
In your linux(es) /home folders, wipe those data folders and create symlinks with the same names (to avoid confusions if any apps are set to those) to the folders in your /data partition.
You can also put your Thunderbird profile on your /data partition and set the path in Thunderbird to your /data partition.
Of course you will have to add your /data partition to fstab in all the distros.
I hope this was not too complicated. If so, let me know.
