I've used mine for about 2 years. Mainly for cookies and quick-breads (like scones and biscuits). They are non-stick without any added fats. Since parchment paper is silicone impregnated paper - think of them as multi-use parchment paper.
Ease of care depends on the brand you buy - but it's easy. Some brands say you can wash them with a mild soap and warm water, some say just wipe with a damp rag, some say just a dry rag. Some say it's ok to roll them up for storage, some say to store them flat.
As for cost ... not all silicone mats are the same. The cheaper ones have a lower reuse rate (say mabye 2,000 uses) and the more expensive ones are higher (3,500 - 5,000). The one thing they have in common is that they average out to about 1/2-cent per use. Parchment paper, on the other hand, ranges between 5-cents to 15-cents - depending on where you buy it and in what quantity.
I bought my daughter-in-law a couple when I got mine (she bakes a lot of cookies for school parties) and she says they are the greatest gift she has ever gotten.