What’s the harm in soldering IC backwards?

So I've been soldering bunch of Xronos boards in preparation for the Maker Fair, and somehow soldered time chip (DS1307) backwards.  Obviously it didn't work, although I had no problem uploading sketch. Then I felt a little heat coming from the board when I was passing my hand over it, and then I touched DS1307... and burned my finger... I'm surprised Chip didn't start smoking :) But what a pain it was desoldering it! Don't repeat my mistake, pay close attention how you orient ICs, electrolytic capacitors and diodes (yes I did diode wrong way too once, with less dramatic results, but it took a while to figure out what was wrong).