The relationship between Second Life populations and real life corporations was kinda tense in 2006, largely because the companies were pretty clumsy in their approach to the world. Their entry looked something like:
a) Create a build
b) Issue press release about being "first (something) in SL"
c) Neglect the build
Not the way to earn goodwill, eh?
However in 2007, perhaps with the help of increasingly savvy interactive design firms, i'm actually starting to see participation that's interesting.
For example this past week H&R Block got involved - sure they did the usual "build an office" but they also created cool items on brand with their Tango product launch. Namely shoes that allow you to dance the tango.
Next the filmmakers behind the movie "300" held an in-world Q&A including the great Frank Miller. I even think someone took of their pants. Yee ha! Author Dean Koontz also did a reading (at a separate event).
And lastly, Diageo did a really neat bar build and pub crawl. Wow, that's totally on-brand and interesting.