I was from Midgardsormr in FFXI, I was part of WeSH for my social outlet, and participated in several endgame shells, including some more specific shells like ShikigamiWeapon.
In 2010, Midgardsormr was merged to Quetzalcoatl. I kept together with WeSH, and a few of my endgame linkshell. ShikigamiWeapon, which was a shell in Midgard that helped people get their Yinyang Robe, was established in Quetzalcoatl as well to help the community.
Did it suck that we lost our world name? Yeah, a bit. But did that mean we didn't have fun together still?
No, actually far from it. WeSH is having a great time on Quetz and picked up new members as well.
The only difference I remember noticing right after the merge was having more competition over endgame content, which is natural due to higher population density. Although as usual, over time some endgame shell dissolves, I join new ones, and still kept in contact with my circle back at Midgardsormr. However, I do not know if they were Quetz shells or Midgard shells or even a mix.
Never, have I personally asked new people I meet in game if they were from Midgard or Quetz, because I could care less. For me, a new face is a new face regardless if where they came from. Never was I ousted from a shell because I was from Midgard and not originally from Quetz.