* It can make moving between jobs harder. Career managers are scared to death of people who are more technical than they are and entirely capable of doing their jobs. Nothing can convince them that we don't actually want their jobs. They will see fit to undermine you at every turn.
* Moving permanently into management in ~10 years seems to be such a common career path that it raises questions when someone hasn't done it. "What's wrong with him/her?"
* Many if not most organizations are stuck in a mindset managers must be paid above those they manage. In some places it's hard and fast rule.
On a related note, one of the worst situations I've ever had to deal with was working for a guy who had stopped being anything remotely technical at least half a decade earlier, but refused to acknowledge it. It made for a fullblown career manager who steadfastly believed that he was still the best and brightest engineer in any room.