The problem is the way it drives a wedge between the player and the PC. It makes it that much harder to get into the mindset of your character; because
you are sitting there making battle plans in the full knowledge that you will be able to choose when to use your daily and encounter powers, but
your character can't possibly know that.
Dausuul said:
Once my players and I get used to 4E, I'm considering offering an optional rule in which a PC's daily and encounter powers are randomized rather than fixed. Something like this: You assign a suit to each of your powers (spades, hearts, clubs, diamonds), and then each round you draw from a deck of cards. If you draw a card whose value is higher than (X), where X is a number dependent on your level, all of your encounter powers of that suit are available for that round. If you draw a card whose value is higher than (Y), your daily powers of that suit are available too.
(Actually, it would probably be a customized deck rather than standard playing cards. But you get the general idea.)
I think you would find that it's a lot of work that generally gives almost exactly the same results. But, if you insist on doing it, here's how I'd suggest going about it.

Have the player put each of his encounter and daily powers on a card (or assign a power to a particular playing card.

Create (or assign) a much larger number of cards that just say "at-will."

Each round, let the player draw a number of cards from the deck. He can use an at-will, or any of the encounter/dailies that show up in his "hand."

Set up the probabilities (cards in deck vs. cards drawn) so that
on average, the player will pull the right number of per-encounter abilities in a 6-8 round fight and his daily once every 4-6 fights.
I think the problem you'll find is that the party's power becomes a lot less "predictable." Some combats (where the players draw well) will be particularly "easy," whereas others will be a lot harder (where the players draw nothing but "at-will" cards).
The "Dail" powers generally won't come into play as often, but sometimes you'll see them twice in a combat.
So you'll increase the swinginess of combat, but, unless you deliberately overpower the characters, you probably won't see appreciable differences in how often (
on average) the powers get used.
Having played with the
Iron Heroes token system, I think it's a lot of bother for a minimal payoff, but I guess everyone has to decide that for themselves.
From what I understand, the WotC guys considered something like this during playtesting (check out the different "recharge" systems in the
Tome of Battle, for example) but chucked it based on the feedback they got. The vast majority disliked the "subgame."
To each their own, though.