In reply to Dominicandave:
Practical questions aren't that unusual in my experience- two I've had were
point out the carb. on a diesel engine schematic. (trick queastion)
For a role on a decomissioning project, they pulled up some rig schematics and asked me to talk them through some of the issues I could see with decommissioning the structure.
I think that they are just an effective way of weeding out folk that interview well but don't "walk the walk" as well as giving a better chance to good candidates with perhaps poor interview skills, but good technical knowledge and know how.
I did also have one interview where they kept asking random maths questions throught to see what my mental arithmatic was like, very effective at throwing you off ballance and putting you under a bit of pressure I suppose!
Cheers,
Stuart