I've had a chance to think about this all day. I still can't decide if this is good or not. The pluses have already been stated by most here. There are some negatives that I've read that are worth repeating.
1) The real loser here is HTC and some of the minor players (Sony Erikson, LG, etc.) Assuming all things remain the same with Motorola, Google is not going to let Motorola put out a bad product. It reflects poorly on Google; even more so since Moto is owned by Google. My opinion is Moto IS going to see some benefits that other handset makers are not going to see (streamlined updates, extra features, etc.) Samsung has enough of a global presence that a Google/Moto relationship isn't going to do much; as Moto isn't as big in other countries as Samsung. LG and the other minor players don't have much presence to begin with. That leaves HTC. They are already under siege from Apple with a possible import block hearing next month. If a Google/Moto phone tops the states, and Samsung overseas, where does that leave them? Ripe for a Microsoft takeover. According to an article I read, HTC already makes WP7. Who else does? Nokia. Nokia does not have much U.S. brand loyalty left. HTC has a better U.S. presence. If HTC feels put off by Google/Moto, they really don't have anywhere else to turn. Losing HTC would definitely hurt the Android community. Their designs and UI push the boundaries for other companies.
2) The other Android players outside Motorola would probably view the Google/Moto partnership as competition. Previously, Google was the open source provider of Android, without any real stake in the individual OEMs, other then seeing them succeed as a whole. Now, the other OEMs could be tempted to diversify their phone line up 'just in case'. I don't see the OEMs putting all their eggs in one basket; especially a competitor's. What is the alternative? I don't see another OS coming in and doing anything. WP7 sales are tepid at best. The other OEMs could invest and begin to push WP7 hard, or revive another open source OS (MeeGo) and introduce that to the U.S.
So what does all this mean? For the interim, I don't see any action from HTC, Samsung, etc. However, I would imagine they are making alternate plans; in case the Google relationship nosedives. I think the next move will be from Microsoft. Apple may be effected, but they have enough cash reserves to battle just about anything right now.
Discussion is welcomed. That was a lot of news articles mixed in with my opinions.