When making a side by side comparison of the keyboards of the Treo and of the G1, the most striking differences are the size of the keyboards themselves and the brightness of the keys when they are lit up. The Treo's key are much brighter than the G1's and this makes a huge difference when operating in low light conditions. When lit up, the keys G1's keyboard take on a dull grayish tint which greatly reduces the contrast between the keyboard characters and the silvery background of the keyboard this not only hurts the readability of the G1's keyboard in low light conditions; even under normal indoor lighting conditions the G1's keyboard can become a little harder to read when it is lit up.
The Treo's keyboard by contrast has always been its strength and is very well thought out. It has two different sets of keys, a white on black set of hybrid number/letter keys which also double as a tiny telephone keypad occupies the center left position of the phone. The rest of the keys have black characters on a pearly white backgound. When the Treo keyboard's bright backlight is turned on, the result is a very bright high contrast keyboard which is easily visible in almost any lighting condition.
The size of the G1's keyboard is deceptive. Or perhaps it's more appropriate to say that the lack of size of the Treo's keyboard is deceptive. While the G1's keyboard is much wider and taller than the Treo keyboard, its keys surprisingly enough are roughly the same size as the Treo's keys. This is mainly because the Treo's keys are packed tightly together and curve subtly upward allowing them to occupy about the same amount of space as the G1's more squarish keys. The Treo's keys are also domed and quite bulbous which makes them even easier to type with. While the size of the G1 keyboard is great, its flat keys tend to cause fatigue when you do a lot of typing on it.
Finally, the biggest change between the Treo and the G1 is the end of one-handed typing. It's easy to whip out a Treo and type away on it with only one hand which makes it perfect for use as a phone which after all is the device's primary function. The width of the G1's keyboard makes this impossible. While the G1 does have an excellent onscreen keypad with nice big keys which can be used to dial a phone number with only one hand, the Treo allows you to use its entire keyboard with one hand. More importantly for people who live in northern lattitudes, the G1's onscreen keypad forces people who wear gloves in the winter to take them off in order to use it. The Treo's physical keyboard (like the G1's) by contrast can still be used even while wearing a light set of wool gloves. Now this might not seem like a big deal at first blush but when the mercury dips below freezing, it becomes a huge advantage.
In the end, I'm forced to conclude that while the G1 does have a good keyboard, the Treo's keyboard beats it almost every way.