There's nothing wrong with the merge join *IF* your tables/indexes can support it. In fact, merge joins can run circles around nested loop joins but again, this only happens *IF* your tables/indexes can support them properly (eg, no need for worktables).
While I can't speak for Jeff I think you're confusing 'merge join' with 'sort merge joins' ... 2 different animals. 'sort merge joins' are typically bad because of the overhead of building, populating and sorting worktables. Eliminate the need for the worktable and a 'merge join' can be quite effective under the right conditions.