I guess it's what people are use too >.>

Nintendo DS (makes all other hardware look like a joke portable wise
# Weight: 300 grams (9.7 oz).
# Physical dimensions: 148.7 mm x 84.7 mm x 28.9 mm (5.85 in x 3.33 in x 1.13 in).

And then there's the original Gameboy.. >.>

Now if I was holding it up to my ear as a phone I would be concerned with its weight. But otherwise it doesn't bother me so I can't imagine the n900 would. Though we'll see if holding it up to your ear for say 30 minutes makes your arm tired.