Anybody watch Grey's Anatomy?
Anyway: I suspect that Izzey's romance with Denny's ghost is actually due to a tumor or some other kind of brain ailment in Izzey's head. This will culminate in the season's final episodes; Dr. Shepard (McDreamy) will have to operate on her to save her life. There will be a final scene, then, before the surgery, when Izzey will say her final goodbye to Denny. That's what I think happens here.
(Although one possible hole in my theory is that the last episode specifically showed Denny sitting beside Alex, with Izzey out of the room. Now, Alex didn't see Denny, but if Denny's "existence" is dependent on Izzey's brain ailment, how could he be sitting there addressing Alex?)
OK, I'm done. Carry on.
(Actually, I'm not done. I think Sara Ramirez, who plays Dr. Callie Torres, is really a very pretty woman, and I think that Chandra Wilson, who plays Dr. Miranda Bailey, consistently turns in the show's best performances.)
OK, now I'm done.