I would not dare put anything in the MBR because if anything goes wrong, I don't know how to restore the old MBR. There is no recovery console, so no way to run
fixmbr
Wow, this is one of the few times I feel knowledgeable on this forum.

I make backups of my MBR and partition table as part of my backup regimen, more often actually as I'm sure you can imagine after a glance at my specs. I run Grub on the MBR for basically every machine I use.
To make a backup of your MBR and partition table:
dd if=/dev/sda of=/mnt/sdb1/sdaMBRandPartitionTableBackupFile bs=512 count=1If you wanted to make a backup of your MBR but not your partition table:
dd if=/dev/sda of=/mnt/sdb1/sdaMBRBackupFile bs=446 count=1To restore just do the opposite:
dd if=/mnt/sdb1/sdaMBRandPartitionTableBackupFile of=/dev/sda bs=512 count=1Hope this helps. The threads linked in my sig may be of value to you as well.
Saikee was my mentor in this sort of thing a while back now. Let me know if you need more input in getting a proper multi-OS config setup.
Edit: The other day I (for some crazy reason) messed with OSX's diskutil...which destroys the partition table every chance it gets, even just changing a partition type. A reboot confirmed my fears. Fortunately I had created a backup using the above posted dd bs=512 command. I had to use testdisk (on PartedMagic, SystemRescueCD, et al) to recover the Fat32 storage partition I had saved the backup to, but once that was completed a simple MBR restore dd command, and I was back in business. So yes, the process works.

The first thing I did after that is email myself that MBR backup file for safer keeping lol.
DrCR
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A5N8X, 3500+ single-core Manchester, 2x512MB Corsair XMS, MSI 7600GT
S-12 430W, HR-05, Scythe Mime, VF900 modded with Scythe 80x25mm. Dual D12SL-12 Yate Loons
WD1200JB, WD3200JB, HD501LJ
Dual, independant WinXP installs via Grub hiding, VectorLinux 5.1.1SOHO, 5.8SOHO.
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MacBook Pro Santa Rosa, 2.2GHz, 250GB Scorpio, Ceramique compound, Pending Appled-Tux Logo mod
MBRed Hard Drive with: OSX, WinXP, Vista (MSDN, pending), Sidux 2007-03
Pending Fusion "bootcamp" VMs pointing to native OS installs