Or... we might just have a lot of experience riding and building bikes and actually know what we are talking about.

So, what is the common opinion on a fixed cog on a freewheel side w/lockring + front brake?

I don't doubt that you may but I can only draw from what I've read over the past 4 years or so for everyone else. I still stand by how I answered the question.

I regularly use wheels with a fixed cog and no lock ring. I frequently apply back pedal pressure to slow down but always rely on my front brake to stop. After all these years I've yet to spin a cog sans lock ring off with my style of riding. This may not be the case when you use crappy components.

I understand that one could thread a freewheel on a fixed hub and that it would still work, but my concern is with stripping the hub. I'm looking to purchase a wheelset from IRO and was considering a fixed/fixed hub but I like to use a freewheel when I do long rides on the weekend, and I'm worried that not having all the threads engaged will ruin the hub (during intense climbs). Recommendations? As of now, I'm thinking that fixed/free is the way to go, just to be safe.

I was a little worried about having fewer threads engaged on a freewheel on a fixed hub, but in practice it doesn't appear to be an issue. I've never heard of anyone having any problems doing it and have heard many respectable people recommend it (such as Sheldon Brown).

If you are definitely going to have a single speed then maybe you should go with the fixed/free, but I've noticed that most people who build up a fixed-gear and put a freewheel on the other side "just in case" never use it (and would probably prefer a fixed cog on the other side).

I did a fixed/free hub and sort of regret it, because I never used the free side after the first couple days. I'd rather have fixed/fixed so I could have a couple different ratios available, but honestly I probably wouldn't even bother with that. Once I found a good all-round ratio for my area I was satisfied. The freewheel (which got a total of maybe four or five days' use) was donated to the local co-op.