Not sure how some of you guys are doing deads, but either way the main joint involved is the hips, not lower back. The lower back in not a joint, and shouldn't be activated like one, but kept tight and straight (slightly arched). If you are attempting to use the lower back as a joint, you're gonna be in a wheelchair soon. The leverage should be transfered throught the hips, not spine. If your back begins to round at all during the lift, you're using too much weight. DLs (not SLDL) are def a multijoint exercise; ankles, knees, hips, shoulders for that matter.
I think the biggest risks associated with DL's are damage from spinal compression and torn biceps. Both are caused by improper form and technique, as well as too much weight. Best to keep midsection and lower back tight, chest out and head up, and knees behind bar with feet flat on floor. I prefer to hold my breath until the bar passes the knees, then exhale. I believe it prevents me from busting a gut. Not straps and no belt.
I don't think deads are overated. It's an awesome exercise for developing the posterior chain, as long as people take the time to do them properly before jumping into heavy weight for low reps. They can be dangerous if done half-assed, but so can any type of lift.