you should never keep your funds on exchangers, especially if you think any fishy stuff is going on there, withdraw your funds as fast as possible (if you can!)
at this point bitfinex offers way too much trading options for people to leave. the alternatives aren't worth leaving bitfinex for. beside that, bitfinex has huge loads of volume every day. if all people withdrew their coins from the exchanges there wouldn't be a market.
I think the answer may lie somewhere between these two views. We have to have money on exchange at various points if we're traders, or even, for many people, if we're simply buying BTC. Post-Gox (at least) we know to consider exchange risk, and to mitigate it by limiting money on exchange, and spreading money between exchanges.
But part of managing risk is adapting when things change or more data becomes available. Right now I don't really know what's going on at Bitfinex. It doesn't feel to me like the last days of MtGox, but that hopeful instinct isn't enough for me to consider it safe for me right now.
I'm not advocating withdrawing everything from every exchange, I'm not really advocating anyone do anything other than manage their own risk. However, there clearly are problems with Bitfinex's trading engine and one way to send a message to Bitfinex that this is not acceptable - is to vote with our feet and take our trading business - and our money - to another exchange.
Edit: apologies, randy8777, I didn't address your point about trading options. That's a fair point. However, I think incidents like this often act as the catalyst for alternatives developing. There are already alternatives to margin trading, though they're not well developed at this stage - I'm hopeful that that'll change.