Well, I had one issue with my magnetic cable holder: an incompatibility between the hot glue and the adhesive on a particular 'model' of holder. The ones with the adhesive and foam backing cleanly separated from the hot glue after a week or so under a slight load. I scraped the foam and adhesive off and reattached the magnet and the holder. I think part of the problem was difficulty in getting the hot glue thin enough before it set--this is a problem when attaching it to metal surfaces, which act as very efficient heatsinks. But other problem is the glue was not too gluey.
I've come across this incompatibility between hot glue and a few surfaces. The ubiquitous hot glue is EVA: Ethylene-Vinyl Acetate, a thermoplastic. I still need to make sure the adhering surfaces are hot glue compatible. It's really more about the convenience of the glue gun than anything else. I suppose I should be using a more universal glue for my generic adhesive requirements.