Van Isle Pilot wrote on Jan 6^th, 2011 at 3:30am:

Yeah this would be a beautiful machine to see from Captain Sim! I wonder if there are any demonstration models still flying? I'd imagine not due to the problems they were having back in the day. Anybody know?

I think the only ones actually flying in a Comet basis (but sadly don't looking that nice though) are these guys http://en.wikipedia.org/wiki/Hawker_Siddeley_Nimrod.

Mark is right, the original Comet suffered from at least two disasters where the plane disintegrated at cruise level because the fuselage suddenly "exploded" as the compressed air inside found a weak spot to exit its prison. There wasn't any sign of weakness before and no chance to be prepared, it just happened "now".
They later improved the structure (successfully) but the market is hard when the thing has the same name as the tragic predecessor and the competitors are already offering completely new planes, also jet driven. So the Comet sales went down.

I think the actual cause for the fuselage problems were some not proper attached rivets (they weakened the material too much) and those sharp edges at the weak spots (which are the openings, like windows) of the fuselage which seem to focus (or "collect") some fatigue forces then and therefore make them strong. Stronger as calculated to happen on the thin aluminum skin.

They undertook quite some time- and money-consuming investigations on these cases of the Comet. They built a huge watertank for the whole fuselage  :o to simulate the constant pressurization and depressurization of the structure and tested it for weeks or so 24/7 until it broke and they could prove the design and manufacturing to be the cause for all problems.

A good but sadly live threatening learning process in aviation industry (you won't see sharp edges on modern airplanes flying high and maintaining a relatively low cabin pressure) there to be experienced on the Comet.
I must admit that she gets even more interesting to be done in FSX then.