I must say that although I am a young SM, like everything I do to be typed, and have ran a successful computer business for two years I will never take digital blocking. I am very good at blocking notation and all of my blocking books have a key in the front. I can guarantee that I can take four times the blocking by hand than anyone can do on the computer in the same amount of time. I got a special keyboard cover that silences the keys on my laptop and I can type quietly, however I do very little during work time on my laptop. I take all my RR notes by hand on my yellow notepad. I will work paperwork during breaks, run sound from my computer, and that's about it. Our job as SMs is to help foster the best possible environment for the rehearsal process. If that means I have to take the time to type something later then I feel that is part of my job. It isn't wasting time if you are doing it for your actors. I am not against using a laptop in the room but it has to be done carefully an respectfully. Limiting its usage is key. If I ever had one of my ASMs on Facebook during work time I probably would ask them to leave the room to be honest.
As far as how I deal with the person being on book missing giving a line, I have a simple solution. When the process starts I create an "on book totem" for that show. Its usually an object like a fancy block of wood or a sticky not that says "ON BOOK" in a bight color. The rule I tell my ASMs is simple: "If you have the totem, you are on book. If you are on book, it is the ONLY thing that you are doing. Since it is the only thing you are doing there is no reason to miss giving a line." Its that simple. If I am on book and I have to do something else I can silently pass it to one of them and they will know that they are on book. I have worked with SMs before where they don't tell anyone to be on book and they do it themselves. Then someone will call for a line and they will ask why I or the other ASM wasn't on book. I have learned that this is the easiest way to remove the errors. I know that was a bit of a digression but it still kinda fit.