I've been using it pretty much since it started, mining 24/7 on a quad and 2 core 2 duo desktops (all 64 bit linux). I've also had about 7 other core 2 duo desktops (again all 64 bit linux) adding to that at weekends. Net result? Very little -- about 0.20BTC roughly.

But as has been pointed out, this is largely due to the inefficiency of the applet used: it's a CPU miner, not a GPU miner.

That said, the 0.01 transaction fees are a relatively new feature, and since they were introduced so quickly, they should have been reversed to 0.0005 equally quickly in my opinion. On top of that, the embedded miner earns the owner about 17% as I recall, so this guy is making a reasonable cut even if it is not a huge net total.

My biggest gripe, though, is that the payout is decreased every 2 weeks, supposedly as an "alternative" to the difficulty increasing. The explanation is that rather than increasing the difficulty, the payout is decreased instead. I have never understood the maths or logic behind that, and from my experiences of watching the mining on these machines, the difficulty indeed does increase (or more specifically, the frequency of payouts decreases) in conjunction with the payout value lowering. So this is a double-whammy: a reduction in payout amount, and a reduction in payout frequency. That annoys me a lot.