Just finished book #5 this morning - The Family Trade by Charlie Stross.

Mini-review: An investigative journalist discovers her family heritage means that she's a "world walker" -- able to teleport between our world and another. In this other world, her family are merchant princes, using their abilities to become rich in both worlds. She's plunged into court intrigue and power struggles. And, ba-ba-bamp -- danger. It's good stuff, especially since Miriam is actually competent.

One annoying thing about the book is that it ends rather abruptly -- it turns out it's half of a longer book, chopped up for various publishery reasons. So now I have to go get the next one.