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Payouts are every hour. 1/2400 of the pool is paid out.

So, each day is 1/100th of the pool?

We vote each proposal just once?
How long do they persist?

You can change your votes whenever you want. If a live proposal is high enough in the rankings during the hourly payout, it gets funded, if it drops down, funding is cut off. Like witnesses.

live proposal

How long do they live?

That's part of the proposal, and I don't know if there is a hard limit. Personally I think this is actually a weakness in the system. There is a 10 SBD fee per proposal to reduce spam, but very long-lived proposals constitute a form of spam as well, and the fee should probably be per-month or something.

In practice I guess UIs will have to prioritize newer/active proposals in some manner. I don't know how that is going to work out.

Maybe they should have a sunset.
Same with witness votes?
If I can leave my proposal open forever the page is going to get cluttered.

I guess tomorrow will answer most of my current questions.

If I can leave my proposal open forever the page is going to get cluttered

Yes I agree. That's why I think the anti-spam fee should have a time component. Perhaps there is a role for multi-year proposals, but most do not need to be that long.