Mango apps are apps which have been recompiled with the new WP 7.1 SDK, which enabled fast user switching. They can also include other, more advanced features enabled by Mango, such as multiple live tiles, but that part is optional.
While Joe appears impressed with the number, given the long run-up I find it rather small, and wonder if in 3 months all of Marketplace will in fact be Mango enabled or not.
Are most of your favourite apps Mango enabled or are you still waiting? Let us know below.
Also see our collection of Mango-ready apps here.