Mal... I agree that the "personality factor" is a big thing. Group dynamics are one of the biggies for marking the success/failure of any trip. So... one consideration is the SIZE of the group you are traveling with. If you have a group of 3 looking for a 4th it's alot different than a single looking for a 2nd. I mean, if you have other people you are use to tripping with, it's less risky to bring along an unfamiliar face. If that new member isn't up to the standards of the rest of the group it's alot easier for the group to "absorb" the problem.... You can alternate paddling/fishing partners, and there are more alternatives for sharing camp chores, etc. When it's a twosome, you're alot more likely to get in each others face. LOL.  
Yellowbird also brings up a good point about reading past posts. If someone makes a post that catches your eye, you can look back at their other posts and get a pretty good idea of who you're dealing with.
I just caught the number of members on qj.... over 450. Wow. I would hazard a guess that half of that number will be tripping with someone new in the foreseeable future, either by choice or by necessity. Maybe half of those will be looking for a partner with experience in the Q or BW. Well.... that's over 100 people. I suppose it would be overly optimistic to expect that more than 1 in 10 of those would be on the same sheet of music in the important areas. But... that still leaves a healthy number of folks to get to know a little better.

CJ -

Bravo!  Bravo!!  When do WE leave?!!

Also, Tripper has made a good point about following a potential paddling partner's posts.  That's what got me in the canoe with HIM, anyway.  I was the big winner on that arrangement, learning more from him in one short trip than on several trips where I was the "most experienced" party member. 

Hey, one other thought.  To calm the fears of spouses & other relatives [who can race to conclusions like:"What!!  You're headed into the wilderness with someone you DON'T KNOW and might be a hatchet-murdering Internet Maniac!"], I recommend at least a brief face-to-face meeting to talk things over.

That's how Tripper did it, anyway... and he STILL let me come along!!

Jimbo   8)

Depends on which way the pink flamingos are headed!! eh Jimbo??

Surely we can come up with ADDITIONAL criteria for the selection of paddling partners??   Jimbo   8)

  I have been on a trip with old_salt before... albeit not in the same canoe....  We shared the same campsite and if I remember correctly he did make a little noise at night  not enough to keep me awake or anything... I was worn out from catching vast numbers of walleye, northern, and the sacred smallmouth bass...  
   I have had three different partners on three different trips... and I am pretty well stuck with the partner I had last year... and although she snores just a little, she is a good paddler and since we just got married I had better keep taking her as long as she wants to go... Although next trip I will have to put her in the stern in a different canoe with one of the kids in the bow, while I take another one with me... We have 4 newbies to break in next June  It's going to be fun  I know...
   But, If I were looking for someone to go with me on a special guys trip, I would have to asked them the three improtant questions that forms the basis of all serious relationships.  Do you love to fish?  Do you love to fish?  Do you love to fish? and I guess I would have to ask a few of the others too that you guys have come up with...  

Bruce

And in relation to what Yellowbird posted above... I am a combination of the Golden Retriever and the Otter