In reply to TobyA:
It's good in both winter and summer and, as with all such scrambles, difficulties are avoidable so you can make it as hard or as easy as you wish. You can then finish off with a circuit of Cwm Llafar, taking in Carnedd Dafydd, Carnedd Llywelyn and Yr Elen before descending via Foel Ganol. In summer there's a reasonable path up the scree to the start of Crib Lem but as others have said, the base of the ridge can be hard to find in bad visibility and snow on the approach slope won't help either. (Hint - it starts higher than you think.)
In descent, there's a good path over Yr Elen as far as Foel Ganol but then it eventually peters out in the molinia. Alternatively you can descend directly into Cwm Llafar well to the NE of Ysgolion Duon or follow the Mynydd Du spur back to Gerlan.
Whatever route you take, it's a good little day out.
Dave