container Mycorrhizal fungi in container growing

How important are mycorrhizal fungi in container growing (mainly asking about inoculation, as opposed to what already might be present)? I've done a few hours worth of reading on the subject, but it's quite extensive. Most companies selling their products containing these fungi lead you to believe that using them will result in what appears to be a 300% boost, in pretty much every aspect, whereas real user feedback seems to show something closer to a 5% boost. Few months back when I was buying the bulk of my growing material, I've decided against buying these products, simply because I was at my budget, and 5-10 bucks for a small sachet that might boost things a bit didn't seem worth it. At this point I'm not likely to fiddle around with it regardless, so I'm asking more out of curiosity.
 
Hope I haven't messed up the terminology too badly. Cheers.

It depends.  This subject ranges from snake oil, to obviously helpful.  It must be qualified.
 
If you're planting outdoors, you will not stop these fungi from showing up.  We may think we need to encourage them, but their arrival is inevitable.   But, we must keep them alive.  That's the harder problem.

You can encourage myco growth by using simple compost.  But you need to also have a big enough, or well enough insulated container, so as to not kill them off in the heat.  When they really get growing, if they die off en masse, you end up with crusty gunk in your container, that becomes hydrophobic, and that is problematic. That happened to me twice last year, before I figured it out.
 
Now, if you're growing indoors, and aren't using compost in your mix, you might want to add it.  I said *might*.  There is some debate as to whether or not packaged myco actually survive well enough to be of any use.
 
For me, compost + AACT will do just fine. The snake oil salesmen will tell you that their products are miracle products, but in truth, it's a naturally occurring phenomenon that you're going to have going on, whether you want it or not.

They may or may not help. Really not a lot of information about the viability of the "propagules" from my research. For a spore to germinate it needs fresh growing root tissue and even better the plant must be colonized from a seedling onward. There are a few commercial mycorrhizae products out there but those are not the ones sold on amazon or "organic" websites. These commercial products are produced by legitimate biotech outfits but unfortunately they are sold on a scale suitable only for agriculture and not affordable or feasible for the hobby grower. 

As far as the scientific literature goes with research on mycorrhizae- they typically get mycorrhizae by growing a mono-culture of a suitable host plant that they can easily produce and then they harvest the mycelia from the roots to inoculate other plants. Sterile plants are inoculated with this mycelia slurry and if the conditions are right they will colonize the seedlings. This gives you both mycelia and spores. As far as I know all commerical products like Mykos, Greatwhite or some of the granular stuff is just spores and dead mycelia. The commercial biotech produce viable mycelia and spore inoculations that inoculate your plants to ensure highest probability of colonization. Really the only way to tell if this stuff works is to examine the roots after some time and physically look for fungal structures and evidence of mycelium colonization.
 
 Mykos and some of the plain jane granular mycorrhizae are just spores so at least you know what you are inoculating your plants with. Some people report good results with these products but I have not personally seen any evidence that any of the plants I have used this product on have been colonized. If you do chose to buy these products I would inoculate your plants as early on in their life cycle as possible and ensure that healthy fresh root tips are in contact with whatever mycorrhizae product you try. Then you essentially have to pray that whatever viable spores interact with growing root tips and the hormones, exudates and plant signaling molecules that facilitate this interaction to occur during that period of viability. 
 
 
I second the use of compost tea and there is a wealth of knowledge out there on how to make a suitable compost tea. If you dont want to make it yourself and have some $$ laying around I would highly reccomend Inocucor Garden solution as its a commercially produced consortium of microbes that have proven in test after test yeild increases, fertilizer input decreases and increased ability to withstand disease. You may have to dial in your compost tea to achieve something that is equivalent to this product and your tea may not be the same batch to batch. I use inocucor because I don't have the space or time to easily produce home-made compost tea to the quality I desire. You can even use this product as a "starter" to produce a more uniform tea every time and to prevent the production of unwanted microbes. 
 
If you want to make a compost tea yourself that has mycorrhizae you can read this awesome manual:
 
http://ecologiesurleweb.free.fr/docs/Docs_agir/Lombricomposteur/Brew%20Manual%20compost%20tea.pdf