I believe btc38 and bter have both indicated that they will be honoring the BitShares PTS snapshots. I'll have to look around for the relevant posts and add them here later. Of course like others have said the best bet is just to have them in your own wallet.
yes they have. I guess it depends on your trading strategy. if you plan on holding them for the long run, then sure, move them to your wallet where they're safe. If you prefer to trade asap then i guess its better to leave them on the exchanges. not to mention that if things follow the path of btsx, people will be able to sell at a slightly higher price once the exchange grants members their shares. This is because withdrawals and deposits will possibly only be allowed later, meaning there will be a small dump and then you will be able to buy again at lower prices