They wouldn't have to brand it as Google. Think: Yahoo buying Flickr.
I also could imagine some pretty terrible things happening to Twitter... like, for example, the site displaying "FUCK OFF" on every page load, forever.
Yahoo! couldn't resist fucking with Flickr, though. Or delicious. Think about the damn tying it to freakin Yahoo! accounts, which look like they're out of the stone age, and the "you have to log in every 2 weeks to save a bookmark" feature they added to delicious, etc., etc. etc.
If people fuck with Twitter like that, it'll be gone. Service instability is one thing. Adding so much friction is another.
Not being a Flickr or Delicious user myself, other than created an account to try it out, I don't know all the end-user effects of the Yahoo acquisitions. But it seems like Flickr and Delicious have turned out alright!
I also could imagine some pretty terrible things happening to Twitter... like, for example, the site displaying "FUCK OFF" on every page load, forever.