According to the rules of LOST, "dead is dead". This still holds true here in Season 6, and the only reason Sayid is alive right now is because...he didn't die to begin with!
According to the Japanese guy and his translator, Sayid was pronounced dead directly after an attempt to save him in the magic temple spring. But come on, these guys aren't doctors...and the real doctor, Jack, doesn't even thoroughly inspect Sayid for signs of life or death, he just starts doing his super miracle CPR work...
...Anyways, Sayid did not drown in the spring, and here's my proof: Hurley is talking to "dead" Sayid, and he notices Miles sitting there shaking his head, with a not-so-somber expression on his face. Hurley says "What?" and Miles sort of nonchalantly says "Nothing". My theory suggests that Miles went to try to talk to "dead" Sayid, but failed to do so -- simply because he detected that Sayid was very much alive.
Perhaps Sayid was just in a dormant state of revitalization, or maybe even "between places", as Charlotte Malkin mentioned to Mr. Eko in Season 2 (remember how she "drowned" in the river, and woke up screaming during her own autopsy??) Another example of a false death is good ol' Mikhail. Mikhail "died" two or three times back in Season 3! "Luckily the pylons weren't set to a lethal level". Not to mention, Nikki and Paulo were both paralyzed by that spider/smoke monster -- the effects of the paralysis were described as so extreme, that "even a doctor would have a hard time" [knowing you're alive, that is].
There seems to be a running theme of characters being not-quite-dead, and staying that way just long enough to convince the audience.
I AM convinced, at this point, that the magic spring did in fact save Sayid's life. I am very eager to see what Sayid may eventually recall from his time out. But that's another theory.
Thanks for reading!