I’m just curious as to what everybody thinks about them. 
I use them in my running shoes for regular training. I’m not competing right now, so I don’t even have a pair of racing spikes to put them in, although I am not sure I would. I do not use arch supports in my cleats during rec football games and I don’t notice a difference so I guess I am not convinced of their “effectiveness” (in quotes because I’m not sure what you want to get out of wearing supports). All I do know is my feet feel more comfortable with them - which may be the most important factor. When you are your own experiment you never have a legitimate control so you don’t really know if a change like arch supports are having a positive impact on something like your joints or posture.
I think ultimately it would be an individual thing. If you’ve ever taken the time to find a shoe based on fit alone opposed to what it looks like or costs, you know how long it can take. I know people who have taken years to find hiking shoes that don’t cause blisters. If arch supports improve the fit for you, use them. Just yesterday a friend borrowed a pair of my year old Sauconys that have added arch supports in them. The second he put my shoes on he raved about how well they fit his feet. I couldn’t believe it considering how old the shoes were and therefore molded to my own feet, but I can tell you that he was instantly sold on arch supports.
As Munkieball said, it all depends on what the purpose behind using shoe inserts is. Is it for injury prevention, injury treatment, or for comfort? Also, what kind of support (OTC, or prescribed orthodics?