Has Hash cash’s time come?

According to an in the New York Times AOL and other ISPs are considering a plan to charge for email sent to their networks.
While unpaid mail will still be accepted it will have to “run the gauntlet” of the spam filters etc.,:

AOL and Yahoo will still accept e-mail from senders who have not paid, but the paid messages will be given special treatment. On AOL, for example, they will go straight to users’ main mailboxes, and will not have to pass the gantlet of spam filters that could divert them to a junk-mail folder or strip them of images and Web links. As is the case now, mail arriving from addresses that users have added to their AOL address books will not be treated as spam.

While I can appreciate AOL and Yahoo’s perspective on this, I can also see this having a lot of undesirable side-effects. Spam filtering is not an easy thing to do without upsetting some people at least some of the time.
It’s a pity that solutions such as hash cash aren’t more widely implemented, as they might help avoid this type of scenario.
You can read about the system in detail on their FAQ, but a basic summary is this:

Hash cash is payment in burnt CPU cycles by calculating n-bit partial hash collisions on chosen texts.
The idea of using partial hashes is that they can be made arbitrarily expensive to compute (by choosing the desired number of bits of collision), and yet can be verified instantly. This can be used as the basis for an ecash system measured in burnt CPU cycles. Such cash systems can be used to throttle systematic abuses of un-metered internet resources.

(taken from here)
Or in plain English.. You basically “pay” for each email you send as your computer has to work a little harder to send each email. The idea being that if you are willing to put in the effort of doing this then your mail *should* be legitimate.
So, could this hail the end of email as we know it? Or will it merely mean that AOL et al will lose clients?