I had used GTS with my Pearl a couple of years ago. I traded some cloned lv100 Deoxys from my friend's Emerald to get a Garchomp, Milotic and Tyranitar, ll lv100, for collection purposes.
A couple of weeks ago, haven't yet figured out how to catch a Ducklett in Balck, I deposited a lv14 Audino in the GTS, and I got a lv25 female Ducklett named ~Aura. Needless to say that it's now a lv53 Swanna, and one of my best pokemon.
I also did a sort of cloning, I traded my Reshiram from my original Black to a Black ROM in my R4 ( for those not knoing what an R4 is, it's a cartridge-like device that has a Micro SD card and you can fill it with ROMs and play them in your DS), then I copied the ROM and its save file into my PC, then I traded Reshiram back to my Black and finally, copying the 2nd Black ROM with the Reshiram to the R4, and traded to Balck, so now I had two Reshirams, depositing one of them, asking for a Zecrom lv 50 & up (since Reshiram was lv53).
When I searched for a Zecrom, each one of them asked for a lv9 & under Reshiram/Zecrom. I don't get why people do this.
Anyway, I eventually got a lv77 Zecrom for my Reshiram. What I want now is a Rufflet, since I really love Braviarys, but I don't have it on dex, so I can't ask for it.=(
In other words, GTS=good.