My 1.5 KH/s earns me about $20 a day here. The same power at LTC earns me $9. Seems legit to me.
Over the last 3 days I've got an average of ~0.0178 BTC per day. At today's rate that's ~$15/day, with 1.8Mh/s (about 1.3% rejects).
Would you mind sharing your address? I would like to see the difference in the patterns, if any?
Sorry the latest graph is only the last few days, and I've been running with one computer broken, so my graph won't be useful.