I don’t know whether you all knew this already, or if someone since has beaten this record, or even care, but I found it interesting. here’s the link:
http://www.guinnessworldrecords.com/content_pages/record.asp?recordid=43451&Reg=1
here’s more unicycling world records: http://www.guinnessworldrecords.com/content_pages/search.asp?searchstring=unicycle
I know those are the “official” measured by Guiness records, but it seems to me that those have already been beaten… Didn’t KH do like a 14ft on Into the Thunder Dragon, and I believe there was a 15ft grind on Defect by Mike Clark… granted I’m not watching those vids at the moment 
The grind by Mike Clark was I think a 16 stair grind
I think
I’m pretty sure most of those guiness records could be broken, or already have been. the problem is doing it under guiness conditions, and with guiness either watching, or having some kind of certified video. I don’t know all the exact rules.
Videos of the grinding and highest drop records…
In case you’re interested, the grind and drop records were set by Alex Toms who posts as “tomsey” here on the forums.
The whole TV segment
13 seconds of snippets
A JPEG preview of the TV segment
I couldn’t find the several threads on the subject of Alex’s records. I’m no good at using the search function. I tried.
Andrew