Because I use my iP4 for both work & pleasure, I continue to refine the layout of my apps. I'm focused on insuring I have only the most important ones on the first screen.
In addition while I've tried quite a large number of apps in the process of identifying what works best for my needs, my priority is the concept of "less is more".
I tend to use my iPhone quite heavily throughout the day, as I'm highly mobile. For that reason alone, I find that folders slow me down. I only use them as a repository for apps I'm testing, or apps I only use once in a while.
To your question of how many, I'm guessing I have approx. 24 that are used frequently each day. Then there are another 30 or so that see weekly use. Finally, I have about eight folders organized by category which contain the rest of my apps.