The RDL is a great builder for your posterior chain, and specifically the deadlift. But I find a lot of lifters doing these improperly, or lacking intent.
Issues range from:
Forward knee travel (shifts the load from the posterior chain to the quads)
Poor control (the range of motion is different every rep)
Poor bracing (causing rounding)
A good RDL should look like:
No forward knee travel
Bar going to the same 'depth' every rep
Mid and Upper back locked in
Hips through on each rep
You should be able to RDLs with 70-80% of your max deadlift, even if you're a sumo puller. It may take time and effort to get there, but it will be worth it.
If you're struggling with patterning or control, try this:
[youtube=http://www.youtube.com/watch?v=dEYmQGkf5bQ&feature=youtu.be]
