It's a proof of stake system, so "a validator has voting power equal to the amount of the bonded coins."
Upon re-reading the paper, I also noticed that it says "In the beginning of the Propose step the [deterministically chosen] designated proposer for that round broadcasts a proposal to its peers via gossip" but it's not obvious to me what happens if that proposer fails to participate. Is the algorithm allowed to skip to the next round? If so, is there some guarantee that the gaps can't later be filled in, and the history retroactively modified? (The DLS algorithm solves this problem by requiring all nodes to propose a value.)
You can prevote or precommit more than once per height (on different rounds), but a commit for a height must be the last signature for that height.
The sudden mass bonding is a problem for light clients doing a certain type of desirable SPV. We're considering options to mitigate this issue. One such option is to throttle the bonding and unbonding at the protocol level, or to introduce a second class of coin for validating and controlling issuance of it.