Well, seems the Lindens are clearing their backlog and delivering today (!) about 300 islands.
Let's calculate a little. For normal users (non educational) reserving a region costs 1.675 US$ and the monthly maintenance fee for an island is 295 US$.
So alone on reserving costs 300 new arriving islands mean: 300 islands * 1.675 US$ = 502.500 US$ income for Lindenlabs. Of course not all of it profit, since they're using these fees to pay the server hardware, plain and simple, but surely are still making some profit with it.
Then 300 islands * 295 US$ maintenance fee per month and per island = 88.500 US$ income on maintenance fees per month with these islands. Most are surely used to pay the staff and the location, but that's where the real profit comes from for Lindenlab.
So - not bad, hu?