"100% pre-issued": Agreed, though Ripple is not XRP.
"arbitrarily distributed": Kinda agreed, not completely arbitrarily (Bitcoin is/was being FAR more arbitrarily distributed). I don't see the bad side of this though.
"continuously managed": Well, only with consensus of the community, like Bitcoin. As RipleLabs holds still a supermajority of XRP, they can devalue the currency at will, act and trade accordingly.
"proprietary currency": I'm not too sure what you mean by that, probably that only one entity controls a lot of it and initially controlled all of it? Again, you confuse "Ripple" with "XRP.
Also what you didn't repeat but what I far less agree with are the following statement(s):
"Which does nothing to change the fact that ripple.com is inherently a centralized and proprietary system, with de-facto and de-jure unlimited control by Ripple Labs (nee OpenCoin)."
"centralized system": Currently, still quite true, as there are few validators besides RL that I added to my UNL. This can and will change though and it already is far less centralized than any other exchange out there, including Localbitcoins with their escrow (=IOU) function.
"proprietary system": Again, I'm not too sure what you mean by that. Every piece of code to bootstrap and run your own Ripple system is available under Open Source licenses. Yes, Ripple is mainly developed by Ripple Labs, that does not make them proprietary. (
http://en.wikipedia.org/wiki/Proprietary_software - maybe you mean "commercial" instead?)
"de-facto unlimited control": For one single instance of fraud, yes. They can probably (with quite a bit of effort) produce a ledger that suddenly does anything they want. This is maybe even true to a larger extent than BTC mining pools doing a huge double spend or rewriting a part of history. It will also have an even larger influence on their trustworthiness and likely sums that were stolen that way wouldn't be released by gateways, similar to the hacking incident at MtGox some time ago. After RL prooved themselves untrustworthy, Ripple would be more or less dead I guess. Combine that with the high chance that IOUs can NOT be redeemed if they screw something up (the only asset in Ripple are XRP, IOUs depend on counter parties! There is no need to steal XRP for RL, as they own far too many of them anyways...) and I personally would say they have a lower incentive to cheat or game the system than e.g. mining pools in BTC (who have only to play by the rules because miners are likely also a bit emotional about how their money is made - if they weren't there woudl be some serious issues in Bitcoinland, like pools gaming Satoshi's dice...)
"de-iure unlimited control": It is Open Source. I don't know too much about this american idiocy of patenting software, but I doubt that this would be enforceable after releasing the software into the public with a license that says: "Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.".