Vicki I always give the hotel shuttle drivers a buck - friends of mine that live Stateside say don't bother, other friends say do it. I can never work the tipping thing out either and it's frustrating, if not annoying, as nobody wants to talk about it if you ask them (the people serving you)directly !
When eating out at a diner or a Denys type place, I look at what others are leaving and follow them. Usually seems to be $1-$2. If it's a posher place, 15-20%.
Porters at hotels I've been told get $1 per bag, but I don't use them as my trusty rollaboard is just as easy in my hands as in others, so I can't comment from experience.

I too am looking at LAX properties, but just for a quickie overnight, so not as particular in requirements as you need to be. Best I've found so far is the Crowne Plaza at USD69 per night.
On past occasions, when I've had all day to kill before the late night flights back to SYD, I've jumped the local transit bus from the terminals up to Santa Monica. Not too far from LAX, great spot, nice beach, good shopping and a pier of entertainment options for the younger ones! I've also cabbed it to Venice (Muscle) Beach as well which was, well, different.