If by random you mean does each card have the same chance of appearing as one of the eight specials on any given day, then the evidence suggests not. There appears to be quite a strong bias, similar to what happens with the daily demo and, as noted by a poster above, the specials concentrate more on older cards.
I've been gathering the data on the specials for the last 9 months as I suspected something like that was happening. In 279 days 2,232 cards have come up as special offers. If the choice were random you might reasonably expect that nearly every card would appear at least once and the most frequent might appear 7 or 8 times in that period. I say 'nearly' all the cards as the newest cards have only been issued recently and so have had less chances to be picked.
In fact 645 (or 80%) of the cards have appeared at least once: leaving 20% that have not been offered on special. Of the 645 that have been offered, 192 have only been offered once, leaving the remaining 453 cards to fill the other 2,040 special offer slots. 68 cards have appeared 10 times or more, including 16 that have appeared over 15 times each. In other words, less than 10% of the cards make up over a third of the special offers.
I've only collected card numbers, but in this thread:
http://www.virtuagirl.com/forumPost.php?foId=3&ftId=17190&forum_search=random
Wszystko o iStripper / Every day, 8 cards are picked at random....?
I have noted the card ratings of 272 cards, offered consecutively by Totem over the last month or so. Each card already belongs on one page of the entire vghd collection, listed as thirty-two small ca...
MoodyCat correlated the card number with the card rating showing a strong apparent bias toward lower ranked cards.
If you're patient then the special offer is still a great way to pick up the cards you really want at a great price, but it's a long way from being anything like random.