In reply to DaveHK:
There has been a trend to not include the letter grade (but this trend is often not applied consistently - not even within the same page of the guidebook!) and to instead do e.g.
5.10- : hard 5.9, 5.10a or soft 5.10b
5.10: 5.10b/c
5.10+: 5.10c/d or soft 5.11a
I was under the impression that the 'ideal' was for the grade to reflect the hardest single move, but in practice to be 'bent' slightly depending on how sustained the climb was.
Another reason to bin the YDS system is that (I believe - opinion alert!) it encourages excessive bolting. Many times I've found bolts right next to fiddly gear (often it's not even fiddly and it's a solid cam), or in the middle of safe and short runouts (2-3 metre or so, nothing to hit). This I suspect arises from a belief that a 5.7 graded route should be safe for a 5.7 leader. In the UK, there's no such belief e.g.
Sunset Slab (HVS 4b) is technically 5.7 or so, but would not be attempted by a 5.7 leader, more like a 5.9 leader.
The 'R' rating seems to be seldom used (I've not even seen one yet at all - only one 'X' route) - either because it's saved for horrendous runouts only, or because the FA doesn't want their route to be unpopular. So what tends to happen is that a bolt or two is placed to keep the route 'within its grade bracket'. This small effect adds up to there being very few satisfying runouts - at least with the more modern routes.
A 'hack' might be to use a + on the R rating e.g. 5.9R- (mild runout, over in a few moves), 5.9R (sustained runout of multiple metres), 5.9R+ (severe runout, falling nearly the height of the crag possible), 5.9R++ (you're going to deck if you fall at the wrong time). But even still, I think that most people want to 'progress' up the grade ladder, and so they will prioritize a 5.10a over a 5.8R - which will still probably leave those climbs in an awkward place where they don't get climbed as much. The UK system really gives easier but runout climbs their fair place at the table, and the YDS just doesn't IMO.