Hi hope you can help

For added security (i.e to stop me loosing it) I've moved my bitcoin wallet to my dropbox (as dropbox keeps backups) and symlinked to it so the bitcoin app can still see it.

Now, does this mean I can now use my wallet from any machine as long as the bitcoin client looks in the right place (via symlink) for my wallet?

What would happen if I forgot to close the bitcoin client app on one machine and ended up with it running in multiple locations? Would that screw up my wallet.dat file?

Thanks