This is incorrect

2G: 115mm high, is 61mm wide and 11.6mm thick, weighs 135g.
3G: 115.5mm high, 62.1mm wide and 12.3mm thick, weighs 133g.

Ask yourself what you need it for, and how will it serve you. Dont fall into the abyss of the typical mentality where newer always equals better.

I believe PeeEl best described it, extending further,
While one might be better technologically, it might not necessarily be better for your application. If you simply want to buy it to look cool, then lol by all means, many buy a car just to look cool and not utilise it to the fullest (Such as running the 'ring in X:XX:XX), or actually jungling a 4x4. Though you should be aware, that youd be severely under-utilising it, should it just be derived from looks.

My advice is for you to wait if and when the new iPhone is released, at least then, you might have 3 options in which to weigh your decision from. If patience is not one of your better qualities, then weigh the 2G and the 3G against YOUR wants and needs.

Cheers