It's also leveraging the fact that twitter (for now) emails the original user to tell them their tweet was favorited. So it's essentially spamming by proxy.
(Also, we've seen this before. It's just follower spam.)
https://en.wikipedia.org/wiki/Spam_(electronic) Note: "indiscriminately"
I wasn't aware of the emails, I haven't received one and I've been favorited before.
The whole point here is that it's a mis-use of a messaging channel - they are leveraging the fact that users _don't_ expect favoriting to be a form of advertising, they expect it to be a message from an actual human being that has favorited their post because they like it. (Similar to the problems with follower spam.)
(I'd also point out that ads on web sites at least help subsidize user's free usage of those web sites, so there is an indirect benefit to the user that isn't there in the case of spam.)
You may have your Twitter notices already turned off - I get emails from them when someone favorites or replies to my tweets, as well as notifications from their app.
Second, the advertising on Gmail (or Yahoo mail etc) isn't an indirect benefit, it's an exceptionally direct benefit. I've gotten to use a truly great, fast, reliable email service - Gmail - for a decade, with gigabytes of storage, and all they've done is run ads on the right side that I've never once clicked on and they never get in my way. Talk about a helluva deal. You're completely correct in the fact that Gmail ads are nothing like spam.
Sometimes, if I really like a tweet, I'll favourite it because I have no other way to say +1 (other than replying to it). But I must like it enough to want to sacrifice the integrity of my bookmarks.
Based on what I'm reading here, it seems that people have wildly varying ways in which they use favouriting.
Twitter would look horrible by partnering with an automated service of any sort.
There are countless bots out there already abusing this idea with followers, and pushing it into favourites isn't making it any better. All it does is add pointless noise to the twitter network and unethically take advantage of the fact that they can't catch all of the spammers at once.
Of course you can make money when you violate the rules, but that doesn't mean doing things like that are an ingenious or stable business model.
Rather ingenious, if I do say so myself. The favorite interaction has become increasingly important over the past year or so... I know friends (non-technical friends) who joined twitter recently who would rather get a favorite than a retweet, as a favorite feels more personal. This opposed to a retweet, which seem to be given out much more frequently than a year ago. It would also be pretty cool to be favorited by a recognizable name. Now that I think about it... could be a pretty useful recruiting tool, if targeted properly.