Personnally up until now I've been using either NTFS or a ext3 fs driver from Windows. I wonder if there's a better way. Probably NAS is the best, but not really practical with a laptop.

There are mini servers, and if you look hard enough, you might find something that suits your needs. However, if a "traveling" server is not realistic for you, and you need access to your files elsewhere from home, you probably need a full server as opposed to a NAS system.

Most of my data sharing is among different Linux distros. The data to be shared goes on a separate ext4 partition that each distro mounts at /mnt/Common. I then symlink to things I want to share, like $HOME/Mail, $HOME/Pictures, etc... Sharing $HOME between distros hasn't worked out well for me.

I run only linux so I've got a few dedicated hard drives (ext4) where I store data. Additionally, I have NAS to share between boxes.

I did set up a separate FAT32 partition on my main desktop when NTFS in linux support was still a bit wacky. Hardly ever used it as far as I can recall.

I nowadays use an external USB HD formatted as FAT32; easy to take with and to share between computers. Might change to other NTFS when necessary.

I have Windows 7 Pro and Mandriva on separate internal HDDs of this "desktop replacement" notebook. Mandriva is the only distro of many I tried that does not automatically overwrite the MBR of the first (Win) HDD. Even when a /boot partition is created and Grub installed there all the rest still write to the other HDD for some bizarre reason.

And EasyBCD did not work with Win 7 a year ago when I went through that aggravation. Even if it did the MBR would already have been scrambled making Win 7 unbootable.

I don't run Windows, just Linux. If I did run Windows, I'd run it in a virtual machine on top of Linux and use VMWare's folder-sharing mechanism to share data between the VM and the host machine.

(I habitually run Linux in a VM on top of Linux. If that sounds pointlessly complex, it's not: it lets me try new distros without trashing my main VM or putting my everyday configuration at risk until I'm comfortable upgrading. It also lets me take as long as I like to upgrade and still have a fully functioning machine at all times. It lets me back up a VM before applying security upgrades; I can then roll back if something breaks. And it lets me connect a small, hardened VM to the VPN at work without exposing my main VM and all my data to the my employer's entire network.)

To share data between my main Linux VM and my Android phone, I use Dropbox.

On my main desktop machine, I have an NTFS-formatted external USB hard drive that I use to "share" data between OSes on occasion. I don't find myself using it that often, though, unless I'm booted into Windows, in which case I need it; it has most of my Windows programs on it. That comes from deciding on a sort of "OS/essentials vs. non-essentials/optional progs" split way back when I was reinstalling Windows on that machine for either the second or third time (this was way before I knew anything about Linux).

My laptop runs only Arch (the first thing I did when I got it was wipe the hard disk clean and install it ), and my other desktop (a clunker with half a GiB of RAM ) runs only FreeBSD (got it from an old friend of my mom's; originally had WinXP on it). If I want to share files between all three, I use ssh/scp to directly transfer them…but I suppose that's kinda off-topic here.