I have been actively following eminis (S&P) for a couple of weeks now and on thursday and friday did a few "test the water" trades.
These are my observations:
They are moving extremely fast and can be very dangerous to trade for novice trader. Think of (JNPR or CIEN) * 10. Executions are instantaneous for market orders but you will most likely be filled at .25 points on top of the usual spread. So with market orders spread is in reality .5 points or $25 per contract. To get out of the position add .5 more for total of $50 + commissions.
This is 1.3% of contract's margin requirement. If you do 10 trades a day you are at 13% disadvantage on daily basis.
If you are using Limit orders you will have to chase the price if it is going in your direction so you will most likely pay more than if you have used market order in the first place. If the price is going against you then of course you will get filled instantly.
You should not put tight stops (.25 to 1 point) because you will always get stopped.
If you are caught on the long side and there is some bad news that is not economics related don't sell into the panic. It is already late. Wait for the rebound.
In my opinion S&P minis should be traded with 2-3 trades per day with stop losses of 2.5 - 3 points and target profits of 5 - 6 points.
I'm using real time audio and I'm starting to realize it's value.
My 2 cents.