In reply to Jamie B: Here's a wee story about lanyards that made me rethink my use of them. (Some of this is a little graphic so beware if you're squeamish.)
A couple of years ago I was belaying someone on top rope on a route that's about WI4. He was climbing with stretchy lanyards attached to his tools. About 20m off the ground he got into a bit of bother and both feet ended up skidding off the ice, leaving him hanging on his tools. Before he could get his feet back on he ran out of ability to hang on and he let go, sagging onto the rope. There was about 30m of rope between us so with the stretch in the rope he dropped about a metre or so. This stretched the lanyard on his top tool out to full extension and the tool then popped out.
At this moment he was hanging on the top rope with a freshly-sharpened BD viper accelerating towards him under gravity plus the tension in the lanyard. What's more, with the lanyard being clipped to his harness, there was little chance of it missing him.
Narrowly missing his face, the pick slashed across the side of his neck about an inch below his right ear, opening up a wound about 50mm long and 8-10mm deep. Amazingly it missed everything vital and there was surprisingly little blood. A bit of saline and some steristrips sorted him out and he got away with another scar for the collection.
My conclusion from this was that, unless I'm somewhere where dropping a tool is going to be a serious problem (e.g. an Alpine route) then I leave the lanyards at home. I view them as something to stop you losing your tools rather than something to sag, let alone drop onto. The chance of a tool popping out or breaking when you take even a short static fall onto it is high (see the photos in Craig Luebben's book for what happens to picks when they're overloaded.)
I know quite a few people have dropped onto their lanyards and everything has held. Please don't assume that this is going to happen every time.