There's a debate raging over on Slashdot about whether an open-source, Linux desktop should be "pure" or whether it should allow proprietary drivers, applications, etc. I know I've helped to foment discussions like this before, but to me the answer to this question is blindingly simple:
No. No, the Linux desktop need not be 100 percent free source.
It's a laudable aspiration, but it's also not something that is practical. It's not a question of whether or not one could conceivably come up with a perfectly free (as in freedom) Linux desktop, but no one has done so yet, so why bother?
Besides, as one Slashdotter rightly notes,
The choice should be with the user, not with the distribution.
Because of the way Linux is architected, a user can make that choice. That's the way it should be, but let's not get bogged down in figuring out how many open-source applications will fit on the head of a pin.
For me, it's not a matter of religious dogma: I use open source because it often works better. On the desktop, that means Adium over iChat or AIM, Zimbra over Exchange, and so on.
But it also means NetNewsWire for RSS, Skype for VOIP, and iTunes for music. Should I care that these are proprietary applications? Maybe I would if the stakes were bigger, as I believe they tend to be for enterprise-wide deployments of CRM, ERP, etc.
But for my desktop, the only one that gains or loses based on my choices of applications is me. I use what works. Hurray! when "what works" is open source. I don't shed tears when it's not.