Natty fails to boot
Thought I better document this, tho I fail to understand a lot of it
Install ATI 11.4 support as I am Dell inspiron 570i
01:05.0 VGA compatible controller: ATI Technologies Inc RS880 [Radeon HD 4200]
Add 'single' to bootmenu to come up in recovery mode and then boot low graphics. I am then told something to the effect 'hardware does not support unity' and told to switch (happily) to classic.
This fixed it. I have run unity w/o trouble w/o the ati 11.4 so suspect it was the culprit.