This is an interesting new trend in rod building that i thought i would post up some info on. Its a really cool idea and pretty amazing cost savings when you look at the benefits. Micro guides are just that - ultra small single-foot guides. Average smallest guide on a factory rod will be a size 5 or more likely a size 6. micros go down to 2 or 3! Here's a pic i took to show the difference

There are some performance benefits to using the smaller rings. First off, they weigh next to nothing - even lighter than recoils. The small, low frames make them near impossible to bend and better yet.. they cost a whopping 1$ a guide for a quality brand.
On spinning outfits, the preliminary information coming out of the rod building community is showing that these things will enhance casting distances - especially with braid and other ultra-limp lines. Due mostly in part to how quickly the ring sizes taper (sz 10, sz 8, sz 6, sz 3.... tip) which tames the wave-lake pattern line takes the form of when it leaves a spinning reel.
The only downside that i can find is if you are intending to use heavy line - 20lb or so - or using braid with a long leader where the knot will have to pass through the eyes. On most 12lb or lighter diameter lines i don't see this as being and issue. A size 3 is so tiny though, on thick lines, i could see it causing and issue.