I have the conjunction and while I do know that the conjunction and the trine aren't the same (the trine is alot easier to deal with b/c there's easy flow of energy between the two planets) but the conjunction can go both ways: either really difficult to deal with like a square/opposition or kind of easy like a trine/sextile.
I know genius is used around casually for this aspect and as nice as it is to hear about it
I think its associated with genius because a lot of people with this aspect like to think outside the box. Uranus and Aquarian energy is associated with breaking boundaries, rebelling against the current structures and systems because we know that current methods can always be improved. Change is scary for a lot of people but Aquarians/Uranians embrace it naturally.
So with Mercury which is the planet of how we think, learn and communicate, when it's connected to Uranus, the planet of rebellions and destroying restricted boundaries, it makes for someone who can really think outside of the box and outside of the restrictions that are placed upon us by society and what we were taught in school.
So the fact that we can come up with things that no one even thought about makes us sound like we're geniuses but really we just have the ability to be original and creative with our thinking.
Now I dunno about you but I've always found that thinking critically on something weird and abstract has been really simple for me, in fact I have a lot of fun just thinking (but it could be my 3rd house stellium talking) about various different subjects aha. Plus Uranus is very intuitive so often times I find that I understand things and find answers randomly and instantaneously without really understanding why. That's often the hard part, understanding why my answer make sense and I have to go back and retrace my steps aha.
People with Mercury-Uranus aspects really like thinking about technology, scientific concepts like physics, occult subjects like astrology (aha that's why we're on this forum).
But also keep in mind that other aspects to your Mercury can modify your Mercury and that still plays a role in how you think.
If you want more in depth information here's a post by one of my absolute favourite astrolgers who gives a very indepth insight into the aspect:
http://astroarena12.blogspot.ca/2015/01/mercury-uranus-aspects-genius.html