You really want to fix those btree problems.
I would start with running the Repair Disk feature in the First Aid section of Disk Utility (Applications/Utilities/Disk Utility).
If that doesn't fix the issue, I would boot into single user mode and run fsck. To get to single user mode, reboot the computer and press cmd-s while it starts. When you get to the text boot screen, type "/sbin/fsck -fy". Do this until it runs without finding any errors.
Finally, if defrag still is giving you btree errors, run the Repair feature in Drive Genius.