I wouldn't ask, if it weren't for Google's Nexus One support forums overflowing with complaints. Ours are pretty patchy with 3G too—so what's going on?
The complaints center around the phone constantly switching between 3G and Edge networks in areas that should have full 3G coverage, getting poor 3G coverage in general, or more often, both. The most damning complaints are the comparative ones. From user firerock:
I have G1 & Nexus sit side by side at my home. I can say that G1 has a better radio/antenna than Nexus. G1 has a solid 3 Edge bar but Nexus only has 1 Edge bar. Yes, I intentionally tested at my home where the signal is weak to see how good the phone can hold onto the signals.
Lest you worry this is a fluke, but the image above, shot by another user, shows the same thing, as do dozens of other complaints.
While the support thread is getting longer, and the whining louder, the evidence is still firmly anecdotal. So, new Nexus Oners: is your 3G terrible? [Google Mobile Help Forum]