At least for you viewer 3 runs for a while! I have a new 17" MacBook Pro and viewer 3 crashes just as it finishes the log in procedure, every time. Viewer 2 was the same. Both work on my older iMac. So come on, Linden Labs, let's keep up with the technology, ok?
On my MacBook I usually run Firestorm, though it's still in Beta and has flaws. Imprudence and Phoenix also work. I think video card compatibility may be behind all this, though I am certainly no expert on this stuff. Meanwhile, I suggest you try Firestorm or Imprudence, and good luck with them!