Electronic – PCB Power Plane Current Carry Capacity

The term that you're looking for (if you want to find more sources on this) is a split plane. It's used pretty often - you aren't doing anything out of the ordinary.

Just a few things to keep in mind:

• You'll want a separate analog and digital ground on your ground plane.
• Keep the planes aligned over each other - don't put your analog power planes over your digital ground. Check out page 4 of Splitting Planes - For Speed and Power.
• Don't route traces that cross the boundaries of your power/ground powers. See PCB Stack-Up - Part 6. Return Path Discontinuities for some info on this.

You might be able to avoid the finger-shaped power planes if you're clever with component placement - in a pinch, you could try keeping the planes simple and using vias to connect the planes to some wide signal traces for the awkward power pins.

Well, I suppose this is one of those topics where opinions may vary. Hower it's somewhat useful to hear opinions backed up by some kind of logic/argument. So here's one from http://www.ti.com/lit/ml/sloa089/sloa089.pdf

There has been a lot of confusion in the past over what is the optimum order for PCB layers. Take, for example, a 4-layer board consisting of two signal layers, a power plane, and a ground plane. Is it better to route the signal traces between the layers, thus providing shielding for the signal traces – or is it better to make the ground and power planes the two inner planes?

In considering this question, it is important to remember that no matter what is decided, there will still be signals exposed on one or both of the top and bottom planes. The leads of the op amp PCB package, and the traces on the board leading to nearby passive components and feed-throughs will be exposed. Therefore, any shielding effects are compromised. It is far better to take advantage of the distributed capacitance between the power and ground plane by making them internal.

Another advantage of placing the planes internally is that the signal traces are available for probing and modification on the top and bottom layers. Anyone who has had to change connections on buried traces will appreciate this feature.

For more than four layers, it is a general rule to shield higher speed signals between the ground and power planes, and route slower signals on the outer layers.

Hope this helps.