Chris Welch at The Verge reports that Google Now will now alert you if a product you’ve shopped for online is available at a nearby store, continuing the proactive features walk along the tightrope between helpfulness and creepiness. The key challenge with this feature is that there often isn’t a loop closed when a product is actually acquired (as anyone who has shopped for something on Amazon and then seen an endless barrage of ads for that item even after it’s been purchased). However, Google has implemented the feature in a smarter way than apps such as RetailMeNot that bombard you with messages about a whole bunch of stores selling stuff that may have no relevance to you.
Making proactive suggestions based on you and your behavior is the essence of Google Now. If you consider it an invasion of privacy or creepy, simply turn it off; there are other ways to get the weather. But over time, I suspect that more people will find its utility outweighs its imposition.