There sure seem to be a lot of sales on Mac software this month. I don't recall quite so many last year. I've already mentioned MacSanta. There are also Give Good Food to Your Mac and a MacUpdate promotion. Are there others?
Of the three, Give Good Food to Your Mac is definitely the most appealing for me. It allows you to decide on your own bundle of applications, with a discount based on the number of applications. Their approach does lead to some oddities, though. For example, you should never buy between 7 and 9 applications, because it is always cheaper to add inexpensive applications and get 10. Even if you'd never use them, you still pay less, and, hey, I would use, e.g., CoverScout, even if I'd never buy it on its own merits.
MacSanta is more traditional in its structure. Unfortunately. New applications are announced every day, with a 20% discount possible for that day. Later in the month, you can still get the applications, but with only a 10% discount. It's a very annoying set-up. I really can't picture buying anything from it at the 10% level, but the 20% level seems only relevant for something that I'd decided to get anyway. Of course, if I've decided to get an application, I've probably already bought it! That said, I have already bought ShutterBug and may well get MarsEdit, too, so they are definitely doing something right. I guess it works to push me off the fence…
The MacUpdate promotion looks to be a good value, if it is offering applications you want. Which it is not, for me.
Update: There is one other point about Give Good Food to Your Mac that I'd wanted to mention. In their FAQ, there is a clear and unambiguous statement that all licenses purchased are normal licenses, with no restrictions. This is the way it should be done, in my opinion.
In contrast, MacUpdate has "full licenses with normal upgrade paths" except for "Swift Publisher, which will be a paid upgrade." Seriously, why?
MacSanta is structured differently, so the issue doesn't really come up there, as far as I can see. You just get a discount code that you use directly on the developers' sites, rather than a bundle through a third party.