I am completely impressed with Windows 7.  I installed the beta version on my home computer a few weeks ago following  hard drive problems that corrupted the Windows XP OS I had been running.  I added a second hard drive to my computer and installed Windows 7 in a 100 GB partition.  When I decided to load all of my apps and switch to ruinning Windows 7 full-time a few days later, I wanted the C: drive to be larger.

To make the change all I had to do was:
<ol>
	<li>Click the Start button</li>
	<li>Right-click "Computer" and select "Manage"</li>
	<li>Select "Disk Management"</li>
	<li>Right-click the C: drive and select "Extend Volume..."</li>
	<li>Tell the Extend Volume Wizard how much space to add</li>
	<li>Click &lt;Finish&gt;</li>
</ol>
The actual change took about one second and didn't even require a reboot - wow!

The key requirement for this to work is that only unallocated disk space that is on the same physical disk and contigious with the existing volume can be used to extend the volume.