In DAoC I hardly ever grouped on my Thane (tank with nukes) or runemaster (nuker). It seemed every character below level 50 was a twinked and powerleveling alt or a BG character. I asked to group a lot and was just rejected. I had the LFG flag on at all times and never got an invite. I just soloed until I got bored and played somethign else. I made a Warden (tank/support/healer, very watery) and suprisingly got invites all the damn time without even looking for them. I got to like grouping but hated Hibernia and the jerk Hib players on that server. My own guildmate stole my gold and convinced the rest of the guild I'd never given it to her even though we arranged it in guild chat. I quit that sorry game.
FFXI is about 90% group based until endgame. Since BLM is a
beloved class in that game it was possible to get invites while /anon to searches and /invisible to your friend list if you were good. I was good. Still, there were slow days... and months. Putting together a group was a chore but I got better results than waiting with my LFG flag on and your comment up, especially while leveling THF and RDM. For missions and quests I had no qualms about putting together a party to tackle them, the problem was a lack of interest or time in the populace combined with stringent party requirements.
NM hunts were the only time I was really shy about grouping. Missions are fun and everyone on the group benefits from advancing. But I waited months to get a moldavite earring because I was too ashamed to ask even my linkhsell for help in getting an item for myself. I finally got it when a pickup group I was in passed by the area just as the NM popped. The shaman's cloak was much harder and I passed the level range where it's useful without collecting it.
In WoW I started at release as a hunter. Not the most group friendly class. By design WoW does not require you to group to advance. The reason to group is to have fun and obtain gear from an instance or finish a quest. Whenever I grouped to complete a quest the group would disband immediatly after the objectives were complete. There was very little gear for hunters to be found in instances and instances were often unfriendly to a hunter's need for space and a clear shot. These two things, and the general player base's attitude and hurriedness, kept me from bothering with instances with that character.
I tried a druid. Lovely class. At the time they could tank or heal effectively depending on the gear they wore and talents they took. I tried to be good at both. And I grouped a lot. Ran instances. I learned that even though WoW is a relatively simple and easy game the average player somehow still manages to suck. I couldn't find a group were 3/5 players weren't clueless and in a rush to reach the boss. I was cheated out of loot by ninja looters more often than not.
Summary:
I like being required to group in order to get good exp and to complete highly rewarding quests, but not to camp a spawn for a single good drop. Games that don't require grouping to advance result in an extraordinary number of players who don't know **** about the game and grouping or are just arseholes because they know there's a good chance they'll never see you again.
Also, I love pick up groups. Grouping with the same people day by day is as boring as soloing.