Carn Dum is not a raid instance but it is a major fellowship instance with many bosses. It is woven into the epic storyline and it is the only place to get some vital class drops (but not funnily enough for champions). As keys must be collected to open access to the stages and as each boss only drops one critical item kinships can be expected to visit CD many time in order to allow their members get all the stuff they need to progress.
I am sure it gets boring after the 10th time but I really enjoy this type of focussed group play. However - setting aside three to four hours to play an instance uninterrupted is quite difficult for me and makes me wonder how much further I can progress in the game. If I expect fellow kin members to spend three or four hours getting my high level items then I need to return the favour - that means running long instances like CD many times and at the moment that creates a difficulty for me.
I mentioned before that I would like to have a go at raiding but as that probably needs even large uninterrupted blocks of time so I will need to be realistic about what I can and cannot do.
Lotro is unusual in that you don't actually have to go raiding to get epic gear. You can buy very high level stuff on the AH given enough gold. However I have spent a good deal of time solo grinding over the last week or so (traits, pages and cash) and I nearly went bananas. I offered my services to the first group I found just to get back into doing group quests.
This is a slightly rambling post but I guess once of the points I am trying to make is that "long" instances can be insurmountable barriers to casual players like me. I love grouping and I love challenging instances but setting aside uninterrupted blocks of time is a challenge.