Again, this was likely due to the minerals in the water causing a short, and after a long period of time, the mineral "bridges" broke/wore-away, resolving the short, and allowing your macbook to boot.
Regarding the "Apple Geniuses", I doubt there would of been anything they could do for you, other than sit there with a cuetip and attempt to wipe down your entire mainboard after a full disassembly. Not to mention water damage probably isn't covered...
That sounds plausible, though I thought any power running through it would've caused it to burn out. I was actually going to do a full disassembly with a mate of mine who was an EE, but never got round to it. We attempted to do it with my iPhone (which was dunked into a toilet in an unrelated incident), but even cleaning everything with isopropyl alcohol it wouldn't work. I didn't hold high hopes for the MacBook.
And no, water damage wasn't covered by warranty, but it was out of warranty anyhow. I just didn't want to pay another $2K for a MacBook Air (maxed out specs at the time).
Regarding the "Apple Geniuses", I doubt there would of been anything they could do for you, other than sit there with a cuetip and attempt to wipe down your entire mainboard after a full disassembly. Not to mention water damage probably isn't covered...