Lots.
First I remember was "Five out over Valley" lots of kit was lost on that Mk 1, about 1966 I guess. There was a two-door cupboard and a 4-draw filing cabinet I was told along with countless classified documents. :0
Then there was a mark 2 oop North on the low level or thereabouts. They climbed to a safe bailout and jumped over the moors. There was a big brouhaha as they needed the AEOs Nav bag with the massive aircraft electrics manual.
Then there was the one that went in near Spilsby.
As far as I know these were all 'premeditated' bailouts, in other words the aircraft did not suffer an immediate and catastrophic failure. I do not know of any attempted bailouts with the nose wheel down.
We did a simulated low level abandonment after a simulated massive bird strike. At 250 kts, 500 feet, the pilot throttled all engines to flight idle and eased the beast into a gentle climb. We maintained a positive rate of climb for a few minutes topping at 1500 feet before the airspeed decayed. We would have had ample time to pack our kit and exit in slow time. The only difference between that and the real thing was the residual thrust of 4 engines at flight idle and no airframe damage.
A rapid abandonment would have had the Nav Rad swivel his seat, pull the air cushion know to push him into a standing position and release his seat straps. Down on the floor he would open the door hatch and pull the door release which would be blown open. He would grab the bar under the plotters seat, swing out and let go.
The oxygen umbilical would disconnect oxygen and intercom and the static line would activate the parachute. Min bailout was assessed to be 150 feet.
There was, IIRC, a secondary door open switch operated by the plotter. The AEO would follow the Nav Rad leaving the way for the plotter whose seat had an inflatable cushion but did not swivel. There were 'London Bus grab handles' hanging from the roof to help pull oneself upright.
I believe there were also successful rear crew abandonments from Valiant and Victor as well. The latter had 3 swivel seats.