first you think that not having an app drawer is weird, but you get over it and do the folder thing. works like the real thing (mine is empty because it was a test and it doesn't bother me really).
battery life on a new sgs2 is pretty good - about a day and a half with quite a bit of use (first charge, but still callibrating the battery).
best thing I noticed is the data connection. on the stock rom I had some issues where it wouldn't do anything and I had to disable and re-enable data and then it would be fine (cell c). with miui, I have none of that. it just works.
all I need now is to get the radio part to work.