As a level 40 cleric, I run 3 points in soothe, with the only healing I have as FF and Sunburst, and I still pull almost the entire dungeon in a boss fight, with a tank-specc'd guardian fighter.
What I'd really enjoy is if the fighter's mark was a bit more like it is in 4e, where rather than making the target more vulnerable to attacks, it makes all of the fighter's allies more resistant to the marked target's attacks.