I certainly wouldn't expect that kind of side effect at all, but maybe it's because I'm used to having a greater degree of control over who gets a claim on a slice of my attention. For me "like" is not a binary concept -- either you like it or you don't. I might like something enough to put it in my bookmarks, but that doesn't necessarily mean I'll want to recommend it to all of my friends or subscribe to its RSS feed. If signaling that I like something will automatically imply "subscribing" to it, then I'd like to be informed about it beforehand.