Naming them does give them more personality. I can't fathom not naming a betta. They are smarter than other fish and more keen to watching details of things outside their tank.
Because they're just fish and I won't have to yell their names out when they get out the fence in the backyard, I tend to give the most absurd names.
My boyfriend and I got an off-white cichlid last week. We call him Yellow Snow. And he has an unusual way of hiding from the dominate cichlids in the tank. He gets under the overhang of the filter and lays on his side. At first glance someone might think he's dead. This is just his hang out. We joking call him Yellow Snow the Parallel Parker. Definitely not something you can shout at your dog without turning heads.
Others have more normal names: Dusk, Pearl, Bumblebee, Fred, Lucky, Blueberry
And we have some more cichlids in another tank with names: Firecracker, CB, Pirate, Wally, Pearl
I have bettas named: Sweeney, Mad Hatter, and the female is Strawberry
Albino BN: Hilton (Paris Hilton)
However I've not officially named my guppies yet at my boyfriends and haven't attempted to name 2 goldfish we plan on rehoming. They've lived in my parents home for about 8 months and never been named.