I have sorted this, but randomly. I restarted a couple of times and managed to erase the disk. But it only appeare4d greyed-out in the finder. I gave it a single partition, and then erased that, and, lo and behold, I had a disk on my desktop. Dunno how it worked or whether it will continue to do so, but fingers crossed...
This information does not pertain to the original Poster's problem, but is being added for folks who get here by searching.
Internal drives OVER 2.2TB have a different problem with ERASE after 10.8.4.
Mac OS X wants to create a Logical Volume group on them, but the rest of Disk Utility does not understand how to further partition it, and it becomes "stuck".
• ERASE in an External Enclosure modern enough to deal with drives over 2.2TB
• Use Disk Utility in any version older than 10.8.4, including the Disk Utility on the 10.6 Installer/Utilities DVD (provided your Mac can boot from the 10.6 DVD)
• Use command line diskutil to delete the Logical Volume Group and the Logical Volume. This may require two terminal windows open to cut and paste the long UID strings from diskutil list in the other window.