2) do other exchanges have security issues? Yes. Are they vulnerable? Only time will tell. I would take Mandelbrot's modeling of insurers (banks are "insurers" of sorts) in "the (Mis)behaviour of markets[0]" to heed: Collapses are levy-distributed with fat tails (infinite variance) so they will happen more frequently than you think, especially if you are operating with a model that uses the normal distribution. Best practice is to diversify.
3) I doubt it. ADDENDUM: But in a rational world this incident (might take a bit of time for the market to realize this) should actually INCREASE confidence in BTC, since a large, irresponsible player was knocked out, and the rest of the players on the field have a net higher level of responsibility (for now).
[0]http://www.overstock.com/Books-Movies-Music-Games/The-Mis-Be...
(I'm linking it via overstock so you can buy it with BTC - which is, hilariously, what I did)