In reply to jwi:
Much of the rock around Rum is dire - really sandy and barely climbable - but there are plenty of faces where the rock is much better, sometimes staggeringly good for sandstone. You can usually tell from a distance which is which by the colour of the rock and the erosion features.
That said, almost all of the longer routes have 'entertaining' sections of designer-crumble, though usually on easier ground. It pays not to be too intimidated by soft rock as long as you're climbing well within your grade. That way you'll be better able to savour the many good pitches, which are often long, well protected and in amazing positions.
Because of the length of many of the best routes (15 pitches is typical), success will often depend more on how well (and quickly) you can cope with the easier pitches, rather than how easy the crux feels.
It's a great place - highly recommended for climbing and cultural reasons. And a wonderful contrast to Spanish clip-trips.