My children have had a good experience with it, through California Virtual Academy. There are definitely hoops to jump through if you go the VA route - testing, turning in work samples, meetings with their "teachers" every couple of months, etc. They've been very good about letting my kids work at their own pace - willingly skipped my son a year upon entry, and haven't really batted an eye that he's done almost completely with that curriculum already and have given us the next year - so my son should be in second grade, but it hasn't been complicated to have him i 4th grade curriuculum. DD has been moving quickly, too, and it hasn't been a problem. Unfortunately, my teacher has told me that they have stopped doing placement tests upon entry and are sending all grade level materials, and then the teacher can evaluate and send more appropriate materials if s/he and the parents decide it's needed. So, it's still possible to work above or below grade level, but there's an extra step involved.
Is there anything specifically that you want to know about it?