I've yet to see a crash, or hold up on system performance using Netflix or silverlight in my MacBook Pro. Flash on the other hand is completely worthless on any OS. Had a kernel panic earlier today watching the MacBook Air boot comparison video via 9to5mac.com.
While the page was loading I was informed that I needed a newer version of Silverlight in order for the page to work (opening Silverlight via Applications yielded no information about a new version being available). Netflix now streams just fine in both Safari and Firefox.