I've noticed that the "hot" tab is full of posts that have about 35 instant upvotes.

What these have in common is that the posts all have the "steem"  and "steemit" tags. So am making this post just to see if my theory is right.

Edit: We're now at the seven minute point - and we have 40 upvotes! Theory proved.

Edit 2: Most of them are "Three-steemers" - they are new accounts with 3 Steem Power. I'm guessing they are upvoting in order to get posts into the "hot" tab.

Edit 3: suggestion to the Three-steemer bots: vote slightly later - at the 16 minute mark - that way you'll earn tiny bits of curation awards which should make your three-steemer accounts bigger and thus have more power.