Can anybody look at this picture and tell me if my japanese maple is
in trouble, and if so, what I can do to help it?

See picture he http://www.tomlucht.com/public/pics/...ellow-moss.jpg

It was doing well last summer, our first summer in this house. This
spring I noticed the leaves are very slow coming back, and others in
the neighborhood are much further along. A closer inspection revealed
that many of the branches have a yellow moss or fungus, in clumps at
the ends and at the joints. On some branches, leaves are coming out
(but sickly), but no leaves at all on the branches with the yellow
stuff.

Is this something I should be worried about? What should I do?

Thanks,
Tom