H&M is selling clothing, which in ads means a lifestyle. The way to market this is not through words but through visuals—people in poses that reflect your brand’s identity (exclusive, chic, affordable, provocative, etc.) In this light, H&M’s approach to Google+ is spot-on: lots of pics of people sporting H&M clothes, together with a quick caption. Even better: H&M includes a link buy the given clothing.
For clothiers, this model is strategic and sound. But the model depends on the brand: while visuals are always important, words—explanatory text—can be just as crucial.
Finally, you’re 100% right: H&M is posting very frequently to Google+. Ordinarily, I’d advise against this inundatory approach, but it’s hard to argue with H&M’s success.
I think everyone is still figuring out Google+—even Google. The metric that’s unavoidable is size, where Facebook overwhelms Google+: H&M’s half-million Google+ friends pale in comparison to its 10 million Facebook fans.
Yet if you have the resources, I strongly encourage you to experiment with Google+. At the direction of Larry Page, Mountain View has been throwing tremendous resources behind this project, and getting in at the still-ground level will allow you to embrace the spaghetti approach (whatever sticks to the wall).
Addendum (2/27/2012): Success!