I use nicknames sometimes, but not always. It depends on what I am using the Pokemon in question for. If it is for in-game teams while playing through the story, random Pokemon caught for the Pokedex or something similar, then no. But if it is a Pokemon I will use for Battle Facilities, post-game teams or online battles, then yes. Occasionally, I also nickname other Pokemon that will be used for other important things.
I will usually nick name some weak pokemon tings like Yes Please or No thanks for when I trade if someone puts something I don't want I put them up or if I do want it I put up yes and then the pokemon I will trade. Occasionalyl I will nickname some random ones too but usually not.
Generally I do not use nicknames there are several reasons for this one is that there are so many Pokemon that it is hard to come up with names for all of them like I used to the other is so many names are banned that it is ridiculous... There are even Pokemon species and character names that are banned all because they contain letters for a word with negative connotation.
I'm actually pretty annoyed that they are forcing us to name Regice in this game...
I nickname almost everything I catch. I just love coming up with names, wheather they'd be silly, smart, cool sounding or referencial....
Literally the only pokes I don't give names to are the ones that I'm 100% sure will have no utility for me aside from pokedex completion. If I have even the slightest doubt that I may use them for anything else, I give them a name, even if it's something rushed and simple as Puppy or Nicky.
Not giving a nickname to a pokemon in the "very important" cathegory (such as a team member in a playthrough) is almost criminal to me XD
I don't nickname all of my Pokémon, only a certain few. That's mainly because I like making my own names instead of simple names. A few examples would be Tyrivicus (Lucario), Hyveru (Eevee), and Kórvem (Latios).
In the past, I usually didn't nickname any of my pokemon. However, since X version, I've been nicknaming pokemon that I competitively train here and there unless they are from another trainer, obviously. Thankfully for the Shiny Machop I was traded, I was able to talk to the guy shortly afterwards and had him rename it to Armstrong.
Normally i don't unless i have a name i find funny. Normally i save nicknames for pokemon i receive in trades so i remember which ones are traded ones. (i have a strange fondness of the ingame trades and other people come up with funny names)
I nick-named my first ever pokemon, a Blaziken who is called Bob whom i got as my starter in Emerald. Aside from that, i haven't really ever nicknamed a pokemon… except a magikarp egg that i got recently in a TSV giveaway with a sub-optimal speed IV who i didn't plan on evolving (as shiny gyarados is much easier to get then shiny magikarp).
Sometimes. I usually don't nickname new Pokémon in new games because I want to get used to and remember their names. I will sometimes for older Pokémon or Pokémon that have grown to have some sentimental value for me but that usually happens when I'm replaying games that aren't "new" anymore.
I don't give my Pokémon names that sound like titles (Crusher, etc.), I usually go for names that sound like actual names to me but aren't common or really sound like fantasy names(Severa, Mercury, Verran,etc.).