I've eaten at this particular location many times (there are several in LA) and was just here again July 2013. Here's my updated Urth Caffe review.
This place is very popular with locals and walking-by tourists and is continuously busy throughout the day. The open air seating attracts many, and it's conveniently located on Main Street Santa Monica, a walking and shopping street with lots of shops and restaurants. It's also only a block away from Euphoria Loves Rawvolution raw food cafe.
Normally, my husband wouldn't choose to come here because it's not as vegan-friendly as he'd like (he's vegan) - there are a couple vegan items, and you could ask to customize a sandwich or something else. Usually 2 or 3 vegan soups each day plus 1 or 2 vegan cookies and sometimes a vegan chocolate cake (good but extremely sugary). During the holidays you can custom order a vegan pumpkin cake.
I like the tostada salad (with black beans), the Mediterranean hummus platter, and the grilled vegetable panini sandwich. The bread served here is artisan style and very hearty.
The best is the soy cappucino. Expensive but yummy.
Cons: long lines, limited vegan