I EV train in-game loosely. I will give a prefference to battling certain pokemon with certain member of the team, and of course use up the vitamins like crazy. But I don't keep track of anything nor look up on numbers. I also use stat-recuding berries to fix them and the power items, let's not have high attack on a pokemon with just special moves.
But I don't look at the numbers.
In-game. Precise EV-training though is a really important part of competitive battling you can't take out.
I have yet to do this although It deffinatly has interested me I want to try, nbut not sure when I will get around to it. I'm not sure why but I have always had this Idea of a Blissey with 250 in attack and special attack and the other 10 ( i think there is a total of 510 points?) put into its hp to make it have some good hp and powerful attack but for the people who actuall ev train this probably sounds like a bad idea
It seems that when I play the Pokemon games, I have a tendency to make a more perfect team. For Diamond, I started planning my team, but in White, I started keeping track of the EVs of my Pokemon get in addition to planning them. Yes, I actually keep track, so that I know who gets more Attack and Speed. Sadly in that game, Attack and Speed EV targets are practically everywhere, so certain places only have specialised EVs, so in the case of needing those, grinding there isn't a bad idea (ex: Stunfisk for HP, Frillish for SpDef).
Oh, when I learnt about EVs, I decided to attempt this on Pokemon to use for Battle Frontier.
I first learned about EV training in the 3rd generation and after that, I've always EV trained my all Pokémon. In-game or competitive, it doesn't really matter. I found EV training much more interesting and it gives a some sort of goal for the whole Pokémon training, that's why I'm doing it in the in-game too. Thought, I'm not so strictly following it while I'm playing in-game - losing a count or battling against a "wrong" Pokémon isn't the world end.
I EV train since 2006, when I first trained my Emerald Flygon for a Battle Frontier team. It was fun to actually start winning with my favourite Pokemon. Today, I mostly train for Wi-Fi teams and such.
As for the story mode... ugh, seriously, is there any point? NPC Pokemon are so terrible (no EVs, very low IVs) that you're gonna beat them no matter what.