I've see a couple around in the last year and by couple I really do mean only 2.
One crossed the finish line of the daytime Manchester to Blackpool ride (2012) as I relaxed on the bank afterwards. Lots of respect for them, whoever they were.
I've also seen one riding up out of Ashbourne on the A515 at the end of last summer.
Nice to see them about, I'd love to have a go but I doubt I'd ever own one.