I would write off Harrison. Even if he does get picked up, I don't see him being very productive, at least in fantasy terms
I would wait before writing off Plax. It will depend on where he lands(I think there will be a team that takes the chance on him) and how quick he gets into shape and learns a new offense. He may be a pretty good sleeper depending on when your draft is.
With that said, I will most likely not be drafting either.
Harrison I don't see offering any consistent value if he is signed, but if he does come back he may have a ok game hear and there. As far as Plax goes I can think of several teams right off the top of my head that could use him, NY Jets, Jax, Balt, Chicago and Minny, just to name a few. I think with Plax it all boils down to what the NFL is going to do with him and what team takes a chance on him, but he can still be a low #1 and a quality # 2 wr. If I could pick either of them up I would look to add Plax for the 09 season. Good luck.