For me, the "Popular" tab on the front page has been broken for the last day (that I've noticed; I suppose it could be longer). The top 25 have been virtually set in stone for the entire time, changing little if at all; neither of the new id games is even there (which is what first tipped me off that something might be amiss).
However, where it really gets weird is when you hit "more popular" at the bottom, which loads a seemingly random mish-mash of games and DLC, many of which are half-forgotten indies that have been out for months, and haven't been discounted for ages; there's even free items and not-for-sale-yet upcoming titles in the list! (Like the top 25, though, this random-seeming mish-mash is fixed, everything appearing in the same order (AFAICT) every time.)
The rankings of games using "By popularity" sort order on
the catalogue page are also frozen, but unlike the front page tab, everything after the 25th title is actually believeable, based on recent sales, releases and pre-order announcements; but it's clearly not up-to-date.