I use a variety of containers, but I am not consistently pleased with what I use. Does anyone have any extensive experience (postive or negative) with fabric pots like GroPots or Smart Pots?

Millet is one of the best when it comes to fabric containers.

I've grown container, and in-ground citrus for a long time. By a huge margin the very best container that I have ever found are RootMakers's air root pruning containers. They are the only containers that I would ever consider using. http://www.rootmaker.com/
Millet (722-)

Folks, I'm jealous on choice of pots which you have there, RootMaker specialy. Nothing like that here, ordinary plastic mostly. I'm tempted to try build experimental pot using wooden planks...

I am pretty sure you can order "air-pots" in Scotland.
They are very good.

I have had very good luck using clay pots and ceder wood containers with my larger trees for a long time. Both types offer a breathable surface which is beneficial for citrus. If you are looking for less weight go for the wood, appearance, clay.

Also, Part of why I grow citrus trees is for there outstanding appearance. wood or clay adds to this, where the awkward look of the air pruning or fabric containers would detract from the trees appearance for sure.

I am not sure what you mean by "not consistently pleased", if you are having problems with your trees, I would absolutely look elsewhere for the source of the issue.

I've been using Rootmakers for the last six months and so far I like them. My only gripe, it seems using them in combination with CHC, the roots are getting colder at night, then my older bark based medium and Terra Cotta pot combination. Of course, the flip side once it's gets warmer could be a benefit.