They are apparently putting off some heat when they discharge, but I check mine regularly, and they always appear to be slightly cool.
Safe storage of LiPos is important, and there is Always the chance of a battery suddenly going rogue and starting a fire, or even a small but dangerous explosive chemical reaction. Particularly during the charging phase? Not sure how the intelligent side of these things work, perhaps they have a tiny fire extinguisher inside them too. ;-)
RedHotPoker