Nothing physical can be trademarked. It's the idea of some features in a particular field that forms a trademark (in this case, the right-pointing triangle, the phrase "Google Play" in the 'app store' field) you break a trademark as soon as 'the typical consumer' might be confused who he is talking to.
So, the particular logo likely is copyrighted, and the idea behind it trademarked. If you redraw the logo (using some artistic expression; a 1:1 copy won't do), you are free from copyright claims, but may still be breaking trademark law.
But this person might land a job at Google, like the Sparrow folks...
That's not an insult, it's supremely awesome that this is even possible and that this dev made it happen. I'm using it now. But there are a few of these types of things for Google Music, there's a similar Chromebook app.
edit: 15 minutes in – it's not extremely polished but I really love it! Finally, no more annoying music.google.com Chrome tab.
To be fair, no native desktop apps. Their android App is great - by my experience much better than Spotify's. And while I do prefer a desktop app to a browser app, their browser app is more feature complete than Spotify's desktop App.
AirPlay audio streaming would also work for me, such as the way iTunes works, but I assume that Apple keeps that locked down as well.
Other than that, this is fantastic!
I use it on Linux and OS X.
The disclaimer is a waste of time. The guy is acting like an idiot and can expect a cease and desist pretty swiftly.
Notifications would be nice too.
EDIT: Actually, isn't it terrible that this is the first thing that we think of? This is distinctly not a problem in the open source world. It doesn't help Google, either. Ugh.
I would like to see an actual native application that caches songlist / artist and doesn't run like shit. But I'll take what I can, I guess. On the otherhand, the Android experience is phenomenal.
But I don't suppose that would be feasible with a Safari wrapper.
Also when I first loaded it, it complained about the lack of Flash, but navigating around and playing music worked just fine.
You're right about the part where they cannot hijack your account, but change data? Sure they can. They can delete all your emails, calendar events, contacts, images on picasa, the list goes on. It has unrestricted access to all Google-services associated with your account.
Otherwise, what an awesome execution; I've been looking forward to an app like this for a while, just surprised Google wasn't the one to produce it.
The right answer is in a sibling comment, Right-click, Open. That way you retain the decision of what's allowed to run.
It's not even an inconvenience, once you've run it, it won't ask again.
Honestly though I'd just use Google Music.
At this point, that's the only thing stopping me from using it. Looks great, but I'm a stat freak and I need my scrobbling.
It has its own Gmail-style chat UI at the bottom of the screen.
Or at least that's my experience with it so far.