I'd recommend looking at PCB Design Guidelines For Reduced EMI by Texas Instruments.

While it is focused on reducing EMI, it offers advice or answers to all of your questions except "Manhattan Routing".

Section 2.1 (about 12 pages) is about Ground and power. It includes these 
useful sections:  


  2.1.7 Power Plane Do’s and Don’ts for Four-Layer Boards
  2.2.1 Single-Point vs Multipoint Distribution
  2.2.2 Star Distribution
  2.2.3 Gridding to Create Planes


It shows how to get close to 4-layer PCB EMI performance using a 2-layer board. Part of reducing EMI is to ensure there is good power and ground routing and decoupling.

PCB's and designing power connections
I have PHP errors redirected to log file. Only for WP installation so this definitely doesn't come from somewhere else. This is what started to come up recently (this is all of them, not cut):

[22-Sep-2010 14:30:41] junk after document element at line 2, column 0
[22-Sep-2010 16:17:08] junk after document element at line 2, column 0
[22-Sep-2010 17:19:42] junk after document element at line 2, column 0
[22-Sep-2010 18:30:19] junk after document element at line 2, column 0
[22-Sep-2010 20:19:23] junk after document element at line 2, column 0
[23-Sep-2010 14:51:40] junk after document element at line 2, column 0
[23-Sep-2010 15:54:33] junk after document element at line 2, column 0
[23-Sep-2010 17:23:02] junk after document element at line 2, column 0


This doesn't really look like PHP error (function blah-blah failed at line x), they are very infrequent and don't seem to be tied to page loads (maybe to some cron event?) and there hadn't been any major configuration changes in months other than keeping plugins up to date and one or two new ones (days before this started).

Googling results are mostly about XML parsing... Of which WP probably does plenty (feeds, updates, what else?..) but how to pinpoint what is going wrong?

This has me really puzzled.
