About Partition for Dual Boots :
The option to have Windows 7 as a Dual boot in MACBOOK is a reat experience for people who came from Windows background. At the same time, there are some restrictions which enforces both these partition live without affecting each other. That is you can read the NTFS files system from MAC OS and You can read the MAC OSX File system from Windows 7. But there is no write permission for both of these. Because apple restricts this to ensure none of the System files are deleted accidently. Good to have.
But the real problem is if i want to move some files from my Windows Partition to MAC partition, then the only way is to copy them to a temporary location (Network, USB Drive etc) and then boot into MAC and move those files. This is pretty annoying but safe when you realize the accidental damage if it has write access.
Why its Dangerous to Partition :
When you have Dual Boot in the MAC either Linux or Windows (BootCAMP) and you need to be precaution that simply creating a parition will corrupt the Hard Disk Start and End Sector Numbers in the Cylinders. This will stop you from booting the dual or triple OS.