A good rule of thumb I've found is:

Divide your KH/s (NOT the MH/s) rate by the current difficulty and you will get roughly the amount of BTC you should be making per 24h at best, assuming that:

• You are running the miners non-stop
• You mine at one of the big 3 pools (Deepbit, Slush, or BTCGuild) where the variance is small. If you mine at a smaller pool, you might get lucky days and unlucky days.
• Your pool is not pool-hopper-friendly. Else you may lose a 10-30% of your possible earnings. See the relevant discussion in the Mining category

So with your 1085 MH/s you should be making around 1,085,000/1,805,000~=0.6 BTC per day at best.