Security of files if my mac is stolen

Yes, it would be fairly easy: the thief would simply have to access your hard drive as an external drive, using either Firewire target disk mode or by removing it and attaching it to another computer's external ports. This would effectively bypass the drive's built-in permissions.

If you store critical personal information on your Mac and are concerned about it being stolen, use FileVault. That's what it is for. If you use it, though, be absolutely certain to have an external drive for backup -- and possibly even a second, less frequent backup to optical media -- as there are anecdotal reports that FileVault can increase the risk of hard drive corruption.

It is very easy to access the files by either booting the computer in target disk mode or by resetting the password using the install disk.

Either use FileVault or create an encrypted disk image using Disk Utility to store the files in.

Quarksta wrote:
I have a login password for my mac but I don't use FileVault or any other sort of encryption. I store a lot of personal financial records on my computer that I wouldn't want just anybody to have access to. If someone were to steal my mac, would the thief be able to access my files (assuming I was logged out)?

yes.

Would it be an easy process?

yes. all they need to do is reset your admin password from single user mode or while booted from the install dvd.
this won't give them access to your keychain and any passwords stored in it but any regular documents will be accessible. you can set up a frimware password which prevents booting in single user mode or from the install disk without knowing the firmware password but that can be circumvented too. the only way to completely protect your data in case of theft is to keep it encrypted. it could be filevault or you could just make an encrypted disk image by hand and keep your sensitive data inside.
That said, vast majority of thieves don't steal computers to get your data. most computers are erased and resold without hours of theft.

Thanks!

I'm not exactly sure how Dropbox works, does it launch automatically when you login or do you launch/login to it separately? If you launch/login in separately an encrypted disk image should work, you would just have to remember to open the disk image first (or add it to your Login items).

Looking at the Dropbox forums it does appear that some people have been successful using FileVault, it might be worth asking there to see how to do it.