I'm still wery green when it comes to understanding mining.
But lets say I have 100mhash, according my calculations it should be about 85shares/hour.
So regardless how lucky, I will always get 85shares ignoring stales and network problems?
So this means one day is 24*85shares= 2040shares.
On a PPS pool before fees I get about 0.05bitcoins/day.
So ignoring fees after 20days I would have mined 1BTC and the share is solid at 85shares/hour ignoring stales and network problems?
It all depends on various factors: downtime, power/network outages, other technical issues etc.
In my experience, 100 Mh/s produces about 1.5 shares/minute, so your 85 shares/hr might be in the range.
Try to find a PPS pool that will work well with your miner software.
For example, I use cgminer and abcpool.co works very well with it.
On PPS, you should earn ~2000 shares/day with your 100 Mh/s. How many BTCs? It depends on difficulty.
If you use p2pool, you might earn more or less. Depending on your miner's luck.