IMHO you guys are over-analyzing this. I generally mount my pannier(s) wherever it is most convenient at the time, so usually my work mailbag pannier is on the left by itself when commuting and my shopping bag pannier is on the right by itself when shopping, and I don't notice any issues when riding, manouevering or standing. The only issue I've ever noticed with a heavily loaded pannier on one side is when parking the bike (no kickstand), I have to make sure the center of gravity is in a stable location before I let go of the bike. Let me also point out that my work pannier is loaded with a laptop PC + accessories as well as my lunch for a toal weight of ~20lb; and when I go shopping I typically filll the pannier with groceries weighing 10-20 lb (of course on larger shopping trips I use both panniers and a fanny pack in addition to my handlebar bag for a total of 30-40 lb).