To me he sounds like someone who is sick and tired of waking up with niggles, aches and strains and has finally asked himself "what's the point of all this" without being able to give himself a convincing answer.
Shane Warne said when he retired that you just know when the right time to go is. Perhaps during the World T20, or even at the IPL, Bond reached that point.
edit: to those bemoaning his retirement a year before the World Cup - Bond has always struck me as the sort of player who'll leave everything he's got on the pitch in order to perform, he could probably hold back a bit, bowl consistently at 80-85mph and still be a bloody good bowler, but it's not in his makeup to perform like that. The mercenary thing to do in that situation would be to continue for a year not putting in 100%.
Without wishing to derail the thread, I wouldn't be all that suprised to see Flintoff retire this summer either. He'll have been living a very cushy lifestyle for the last 6 months - ok, he's going through rehab, but he's been in Dubai, with nice hot weather and will have been able to spend some quality time with his family, and has started some media work with his panel show on Sky. The first time he plays again for Lancashire, and wakes up sore the next day, it wouldn't suprise me at all if Flintoff asks himself what the point in him continuing is - if he makes his way back to full fitness and the England LO set up, there's potentially 13 ODIs, plus 2 T20Is this summer, as well as 7 ODIs and 2 T20Is in Australia, before a long, gruelling World Cup and possibly IPL in the subcontinent. It wouldn't suprise me in the slightest if at some point in between, Flintoff questions what the hell he's doing when he's had such a cushy lifestyle for the past 6 months.