Dana VanDen Heuvel makes a good point about corporate blogging:

If companies think blogs are important, then they should respect the bloggers and listen, optionally engage intelligently and individually but they shouldn't try to persuade through advertising, as the old joke goes, it wastes your time and annoys the pig.

Very much so, I think. You want to have an honest conversation that engages the other party, not a one-way blab-fest. Prospective listeners get enough of that already - act like it's TV advertising and they'll tune you out and find something worth listening to.