How do I check if a file is a symbolic link to a directory?

Just combine the two tests with &&:

if [[ -L "$file" && -d "$file" ]]
then
    echo "$file is a symlink to a directory"
fi

Here is a single command which will recursively list symlinks whose target is a directory (starting in the current directory):

find . -type l -xtype d

Reference: http://www.commandlinefu.com/commands/view/6105/find-all-symlinks-that-link-to-directories

A solution with find and using a function:

dosomething () {
    echo "doing something with $1"; 
}
find -L -path './*' -prune -type d| while read file; do 
    if [[ -L "$file" && -d "$file" ]];
        then dosomething "$file";
    fi; 
done