It may not hurt you to drop from five days a week to three, but go less than posting to your blog three days a week and you will definitely lose readership and subscribers. It is definitely a tough road to hoe to build back up after you have had a significant drop in traffic. It takes time posting five days a week and great content.
Once you have arrived at the level of activity that you desire, then you need to balance the time you expend on your blog with your other business needs. This is what I do. When I had started posting sporadically for nearly six months due to personnel issues and sheer blogging burn-out, my traffic took a dive. To rebuild, it has taken will power and work. For over four months I have now blogged five days a week and now I am simply ready to move back to three days a week. Typically I blog ahead and do one week ahead on Saturday. If I find something great to write about in the middle of the week, I just do an additional post. If the post is not time sensitive, I will simply use it as one of my write ahead posts.
Personally I found blogging five days a week exhausting. For professional clients typically we will break a five day a week gig into a project for two writers. It is simply tough to consistently write great content every single day on one topic. Try it for an extended period and you will understand what I mean.
If you post less than three days a week some portals like My Yahoo will collapse your RSS feed on the page and post a note saying “no new posts in the last seven days” even if this is not exactly true. Post on a Monday, Wednesday, Friday schedule and feed collapse is prevented.
So should you write three, four or five days a week? I recommend if you are starting your blog five days a week for the first three months to build content and readership, then cut back to a long term plan of three days a week to maintain what you have and not lose headway.