We didn't have a problem running any of the Windows 7 editions on netbooks, including Ultimate.
And while some manufacturers may shave pricetags by only giving you Windows 7 Start edition, we expect most netbooks to come with Windows 7 Home Premium.
We ran some real-world benchmarks on an Asus Eee PC S101 to see how Windows 7 matched up to Windows XP on low-end hardware. As you will see, Windows 7 is actually quicker in most cases.
Here are the results: