A very small example that surprised me, was a few months ago when I installed Taskline and mentioned it on my blog. Since then the guys at Taskline tell me they've received a number of downloads of their software from my blog post. No epidemic yet, but who knows who else will read that blog entry and post on it themselves.
At the moment there are lots of bloggers talking about new products like LookOut. By the way, I installed LookOut last week on my laptop and it rocks. It's the fastest way I've found to search through my mail.