Apologies for wandering slightly OT.
Simons first link to the article describing the trip was what instigated my first through trip in '96. My writeup has some pictures of the condition of the bridges etc in those days.
http://www.cowdery.org.uk/rctrip.php (ignore the first link to photos, it's broken. They are further down the page).
Importantly, we'd verified the Rhosydd end of the trip beforehand to ensure we could get out of the lake, and always make sure we could retrace our steps.
On another occasion we were overtaken by two lads with no helmet, just a head mounted light, outdoor walking clothes, figure 8's and a small bag with a dingy. They did the trip in a couple of hours. However, they had absolutely no contingency for problems. They had to either make the trip or sit and wait to be rescued.
I think the key point is that although the trip is fairly straightforward (if you are suitably equipped and know the way), it can rapidly change to an epic with the tiniest issue arising, even as simple as not being able to navigate sucessfully across the moor in the fog & dark from Rhosydd to Croesor! (sounds like it wasn't just us that had that small issue!)
Chris.