I'll pull out a couple of boats later this morning and snap a few pics. Not 'perfect'examples - I keep thinking of changes with each boat - but they might help.

I'd appreciate that - I'm having a real hard time finding good references online. Even where the lines are clearly visible, it's hard to tell how they're attached, etc.

I'm more concerned with the perimeter safety lines, which are never bungee (elastic shock cord) on well-rigged boats. Anybody who has grabbed a shock cord instead of the (adjacent) deck line during a rescue will tell you that bungees don't work well for handholds!

Definitely - that's why I was thinking the commercial boats aren't necessarily good examples, because I THINK they're using the same line for both, so they're working against a different set of requirements regarding the "ideal path."

Any recommendation on rope, btw? Would 1/4" Sta-Set (2500 lb breaking capacity, 89 cents a foot) be ok, or better to upgrade to a fancier fiber like New England Ropes HD-75 with a 9700 lb strength at $1.29/foot? Seems like hand feel is as important as breaking strength - is 1/4" too small for grabbing?

You'll need to adjust the lines as they invariably stretch after a few uses, so splicing wouldn't work very well, IMO.
That's not what I meant - I'll try to explain better in a later post.

I was envisioning the "tensioner" as a way to overcome the stretch issue. Picture four web loops, two at the stern and two a foot or so back from the bow, so the perimeter loop forms a rectangle. Then another line is tied to that perimeter line on the short side of the rectangle at the bow, and pulled forward to create a triangle, tensioning the entire loop, then tied off to the "eye" in the bow. (of course real installation would have more web loops, so not actually a rectangle) Thought I saw a photo of this somewhere - that's why I thought it was what you meant.

Alternatively, the tensioner could be at the stern, with a jam cleat or something, or actually could be a turnbuckle, or each side could be a separate line with a tie-off or turnbuckle, but I'm trying to keep it simple. I'm assuming I don't want too much tension on this line anyway, right? Not floppy - but certainly not bar-taut.

One ongoing problem for me has been the optimum spare paddle attachment system. I've been convinced that a paddle bag (Nigel Foster style) on the aft deck is a good solution. Spare paddle stowage, location for chart and deck compass, and possibly items like GPS, waterbottle, paddle float, and pump are things to think about when deciding on deck rigging.

That's a big reason I'm strongly leaning towards web loops rather than something built-in like a maroske - I'm sure I'll want to make changes and additions down the road.

Thanks for the detailed response!