We use CEX.io / Ghash.io
Not a great amount, 46GH/s managed, and 4.5GH/s in 2x Antminer U2's on Stratum.

It gives us a steady return to spend on our advertising. Not much, but with Btc price rising as well, it seems fair.

We have no issues with site trust, or the costs of maintaining Gh/s, these seem realistic enough to maintain this as a going concern, in fact it's the sites that offer unrealistic returns that are most likely to fail.

If a mining business doesn't cover it's running costs, and make a reasonable profit, it will fail.
If a mining business gives unrealistic returns - It probably has a bad business model and will fail.
If a mining business offers ridiculous rates of return - It probably has no mining kit, so Just don't go near it.

CEX.io and Ghash.io are realistic in their maintenance prices, and that gives us confidence.
Theres an old adage -
If you spend too much, you can often lose a little money. If you spend too little, you can often lose everything.

ViK - Project Lead, Badbitcoin.org