I agree with both of you... I was giving this a few days before I added my two cents... but... I really don't think ANY form of marketing should be ignored. Even if it is something that doesn't always directly drive sales, it can ALWAYS help brand your business... plus, if your business is linked back, then you've also created another LINKTO: resource for SEO... Google sees your site yet one more time linked in conjunction with relevant content.
ALSO... Customers (or potential customers) start seeing your business name/logo when they're just playing online... and then maybe eventually become shoppers of your site or bookmark it for later. It's just that they can begin their name recognition that much more easily if you're actively being a part of the whole online community.
I wanna go check out Threadless.com - sounds cool... and I myself just posted a bulletin on my personal MySpace about how I need T-Shirts... My own little marketing scheme to get free t-shirts from all the bands who asked me to be their "friend".
I'll let you know how it works out.