In regard to placing the personal item under the seat in front of you, bearing in mind most of the time I am in 1A so the FA takes my handbag to store it during take-off and landing, when I have had it under the seat in front of me my handbags require cleaning on a regular basis. The area where people's feet go are not clean and often are quite nasty as they are not deep cleaned after every flight (or even on a regular basis as far as I am aware). For the guys that may not be an issue for black backpacks but my expensive leather handbags take quite a beating. I suspect the overheard bins are not cleaned on a regular basis but the floors are quite filthy. Just another consideration why folks with their backpack may want to put them in the overhead bin, and also things are spilt all the time and I often end up with my handbag bathed in some liquid substance that is unidentifiable - a third world problem but a recurring expense for me. Yes, I am a lady so carry a handbag.