First of all, I have noticed in the many years that I have been flying, that people who refer to it as a "walkround" do exactly that. Most of us have probably seen them - a casual stroll out to the aircraft, a brisk walk (clockwise or anticlockwise does not seem to matter), waggle the control surfaces, peer under and over the airframe, perhaps undo a fuel filler cap and peer knowledgeably into the fuel tank, then climb aboard. If they happen to be an instructor and the student is in the aircraft at the time it merely goes to show (in their own minds), how much better and more efficient they are at doing what someone has already done. Irrespective of how well someone else may have done the check, such arrogance and posing will rarely, if ever, bring to light a missed item.
The procedure I suggest that we should all be adopting should either be known as a Check A or an external check of the aircraft. As a 23 years experienced instructor I never refer to it as a walkround to my students, as this tends to lead them into doing just that.
I cannot fault those who have an accomplice do the checks as well. A second opinion never hurts. All I would suggest is that both parties do the complete check. I know from personal experience from way back how two people doing half the check can make disastrous assumptions. In my case it resulted in nothing worse than getting airborne in a Canberra with a mainwheel undercarriage lock still in place.
It is interesting to see the difference in attitudes between pilots going out to fly and those same pilots attending the PFA rally and having a go at the external checks of an aircraft that they know has been rigged to have some faults. If only we would all do the external checks/check A with the zeal and thoroughness of these individuals it could be that the accident rate worldwide would come tumbling down.
Bottom line, I suppose, is to be thorough and meticulous irrespective of the weather. In the absence of anything else then the manufacturers check list is as good as anything we are going to get.
Enjoy your flying folks, and fly safe.