I’ve seen many people asking and discussing this question online, but the issue has been somewhat confused. The question should not be, “How many TOTAL tweets/day?”
@replies are only seen by followers of both parties, so I don’t consider this spam. Instead it should be viewed as having a conversation within a closed circle of friends. The real question is RTs (re-tweets) and OTs (original tweets).
You should keep a very tight reign on RTs. Too many RTs/day is going to get you unfollowed real fast.
But OTs are much different. You have some leeway here. I am much more interested in what you have to say than what other people are saying or even what you think is interesting that other people are saying. That is why I am following you instead of the person you are RTing. The occasional RT may persuade me to follow that other person, so only RT their very best content.
Rules of Thumb:
1. No limit on @replies, but use your better judgement.
2. Keep RTs to a minimum. 2-3 RTs/day tops. (Unless you are a professional blogger/writer who lives online.)
3. Maximum of about 5 OTs/day. Maybe 1 less if you RT often, maybe 1 more if you never RT.
1. Everyone has a bent toward either quality or quantity. Be willing to push yourself to the middle ground that maximizes both.
2. It’s OK to go an entire day without tweeting.
How much do you tweet?