Jaguar's problems stem from Nasser's stupidity of trying to make Ford a conglamerate, forgetting the auto end and the current administration conservative, no-risk-taking mind set.
It was stupid to try to sell a reskinned Ford Mondeo as a Jaguar X Type. Its a good platform but not good enough that anything could be done to it that would make it handle, ride or perform like a true Jaguar. It was also stupid to try compete with BMW and Audi model for model, the reasoning behind the X Type in the first place (a lower price entry model). Jaguar is expensive and exclusive, if not in price, then by production.
The S Type has gotten long in the tooth and Ford management neglected it for far too long. It should have been updated this year or last, not 2 years from now (2008MY).
The XJ is suffering from the same thing that is killing the Five Hundred, its too damn boring. They took the very elegant lines and proportions of the Series III/X300/X308 and bulked it up. Unfortunately, it threw off all the proportions and destroyed the gracefullness of those older designs. They needed to break with the past and built something more "conservatively radical". They should have kept some design cues from the past but taken them in a new direction.
The XK is beautiful but it looks too much like an Aston Martin. AMs are muscular and beefy in their look, while Jags are supposed to be sleek and light, like the old E Type or the XK its replacing. The new XK looks like an upmarket streetsweeper, the R model doubly so. But I'm sure it will sell well.
I don't think Ford should cut Jaguar loose any more then Land Rover or Aston Martin. They are excellent halo cars, much like the Ford GT. They dovetail well with Ford's history with England. What Ford needs to do is keep their mitts out of them and let them get on with it. Let there be tech cross-pollination, like Chrysler and Benz, but let the Brits design their own cars. They know how to do it better then a bunch of Detroiters.