Going by this really good analysis...
But Apple's stuff is built more solidly than the Nexus: aluminum, steel, and glass rather than plastic.
Redoing Gruber's weight estimates by calculating the Grams per Cubic Millimeter, the iPod touch is 0.00215 g/mm³ and the iPhone 4S is 0.00223 g/mm³. Multiplying that by his estimated volume comes out with a weight between 416 and 432 grams if it had a similar weight-per-volume as an iPod touch or iPhone.
On this list, that puts it around the Kindle Fire.
Doing similar with the iPad 3, it's about 423,557 cubic mm. For 0.00154 g/mm³ (the iPad 2 gives a virtually identical number, which is another good confirmation on this weight-per-volume method.) Based on those two, it gives a potential weight of 298 grams.
I'd guess that just about 300 grams is a pretty safe estimate, and not far off from the Gruber's original 265 :)
(updated to show correct g/mm³ unit label.)