Whereas I didn't experience problems like this, I've seen a thing or two that make me wonder how ready Google's infrastructure is for the massive influx of Android users.
A couple of days ago, I've bought the second G1 - my wife didn't like black, and I got stuck with it, and the process of changing the phone identity on top of that.
So she just took the shiny new phone, booted it up, logged in (with the identity that she had used on the old phone for a month), said "Yep, it's on" and walked away.
I've spent about 30 minutes trying to figure how to disassociate the phone with the GMail account (all this time the phone was still operable, I could place and receive calls, and everything worked except for Email and IM). Haven't found a way (manual didn't help either), decided to do a master reset and...
...got stuck for good.
An attempt to sign in caused a lengthy delay accompanied by the warning that it can take up to five minutes.
In reality, it took about two to three hours, with multiple timeouts and invitations to retry and check with T-Mobile whether they provisioned the SIM card correctly.
As I was close to the T-Mobile store, I asked them - and they told me that all recent customers are having this problem, quote, "it takes from three to twelve hours for the activation to work".
So I went home, hoping that this problem would dissolve by itself, and it did - like I said, somewhere between two and three hours since the first attempt.
Of course I've been wondering what went wrong. The only explanation I have at this time (and I don't think Google or T-Mobile will be offering any :) is that Android authentication and mail access are not handled by the same infrastructure as GMail. My best guess is that the activation delay is caused by account replication - and yeah, good luck replicating a few years and gigabytes of my mail, along with countless others'.
This, along with HTC's updated forecasts, makes me wonder if the omnignostic Google flopped in demand predictions, or was it T-Mobile that can't cope with the load.