Below is a photo of my original iPhone next to my new iPhone 3G.
The original iPhone (on the left) is still running 1.1.4 (4A102) whereas the iPhone 3G (on the right) is running 2.0 (5A345) which it shipped with.
The first thing you might notice is that 2.0 has fixed the problem with the stopwatch taking up too much space when it goes over 1,000 hours (although not the lap time)
You might also notice the colour temperature difference (the original is more blue, the 3G more yellow) that has been much talked about.
But other than that, they look pretty similar. Except that's where it surprised me. The stopwatch is almost the same on both: about 2,200 hours. But that's three months and the 3G only came out a week ago.
That's right: when iTunes synced the data between my phones, it kept the stop watch going!
As far as I can tell, the 1.4 second difference is actually due to the clock in the iPhone itself not the stopwatch specifically. If the old iPhone could still sync its time from the cellular network, the two might show identical times on the stopwatch.