Played quite a lot of Vi over this weekend and I have to say I find her very enjoyable. Her skillset is just fun to use and her whole character is neat. I actually prefer to jungle with her then top lane and that is just because there are just so many other top laners that I don't think she can handle since she doesn't have any sustain. Her passive shield helps a bit in lane but her kit just works so well in the new jungle. Q and E basically finish off all the little creeps super fast and your W will proc on the big creep and you kill it much faster.
I've been going Machete + 5 pots > Madreds > Boots1 > wriggles > brutalizer/boots2 (either Swiftness if they have lots of slows, or otherwise mobo) > black cleaver. Then start to build tankier either going aegis > bulwark for the MR or if you need some more armor go either Locket (This item gives sooooo many fucking stats and the shield is pretty awesome too for team fights) or Randuins.
Swiftness boots are awesome because not only do they make your Q slow less, but they make you overall faster then a lot of champions. Mobo boots are amazing just because they help with ganks much more, allowing you to hopefully lead in with a Q rather then having to burn your ult asap. Ganking through the lane with mobo boots is very scary because you can either Q into R to gap close onto an enemy or can even flash > ult since the range is long enough.
I'm still unsure which skill path is better. I've done the Q max first and I've done the E max first. Reading the skills it feels like Q max would be better no matter what since the CD gets a lot less and the damage goes up a lot more, although I like the E max because it does a little more damage and you get more charges off sooner (it's like every 6 seconds iirc?) plus it's a much more guaranteed hit where as if you max Q and either can't charge it the full way, or they dodge your Q you're shit out of luck where as they can't dodge your E. Plus the splash damage the E does is pretty amazing in team fights. I think the past couple games I've preferred going the E max in the jungle just because you'll usually always have 2 charges every time you get to a new camp which lets you clear it almost instantly.
So, EQWEER, R > E > Q > W. (I have yet to try out a W max, but I don't think it'd be that great)
So anyway, super fun champion imo, although I don't care to use Vi for top lane I absolutely love her in the jungle.