But how did pinned items originally come to the attention of consumers?  Google, email, blogs? Pinterest itself? 

Vision Critical found that 50% of the items caught users' attention while they were casually browsing Pinterest itself (24% on a stranger's boards, 19% on a friend's, and 7% on a retailer's). Another 10% came from Pinterest searches. These numbers are a testament to Pinterest's power as a kind of user-generated digital retail catalog that shoppers flip through for ideas. 

Unlike traditional showrooming, which is spurred by e-commerce giants like Amazon and eBay, reverse showrooming seems to have its roots in social media and  social commerce: friends' and strangers' recommendations can inspire shoppers' purchase decisions, offline and online.  

I regularly get bored with Pinterest these days. Am I unusual?

The data suggest that.