I'd definitely take it if I could top myself. If it would make me truly immortal, that'd take a little more consideration. But I suspect I would still go with it.
About the only thing which would hold me back from the latter option is what DEFRON pointed out earlier: the possibility of being stuck somewhere http://tvtropes.org/pmwiki/pmwiki.php/Main/AndIMustScream.
As to watching people around me die off... well, that'll happen anyway (assuming I last a decent time), and I'd have decades to work on coping skills before it'd be a significant problem. Long as I kept building new relationships I'd still have a network of friends to support me, too. The way my memory works might help, too (sorry, too tired to bore you with an explanation).
It might svck to be stuck as the current flavour of human while humanity as a whole evolves, but I reckon the time-scale on that would give enough time to get over inferiority issues

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So, having covered some of the cons, what are the pros for me? There is so goddam much I want to do, see, experience, learn! One lifetime is nowhere near enough -- not even for just the stuff I could do on Earth

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