I've never left Anya with anyone because we haven't really had her long enough. And even then we're going on a mini-vacation in october and away for Christmas in December and we're taking her with us both times. Not only do we not have anyone reliable to pet sit, but I worry too much.
I've pet sat twice for extended periods, for two very different people:
1. My friend left for a week and brought her two cats to my apartment and left them. She verbally gave me instructions, but nothing detailed. We winged it and had a pretty good time. Of course one of the cats didn't start adjusting to our place until the week was almost up.
She's a very timid cat anyway though even in her own surroundings.
2. We house/pet sat for almost 2 weeks. We met with the couple and got verbal instructions and a walk-through AND a two page letter with detailed instructions signed by the whole family including their two cats and dog.
I much preferred that way. The animals were happier. We were happier. She even left us with highlighted maps for different trails to take to walk the dog and to get to several of the closest animal hospitals.