Continuing with the general theme of Func<>, Action<> and generics here is a nice little trick to replace long but simple switch statements. Often in your code you will find statements like this:

switch (category)
  case Category.Articles:
    DisplayBox.Text = "There are " + GetArticleCount(user) + " articles";
  case Category.Posts:
    DisplayBox.Text = "There are " + GetPostCount(user) + " posts";
  case Category.Comments:
    DisplayBox.Text = "There is " + GetCommentCount(user) +
             " comments on " + GetPostCount(user) + " posts";
  case Category.Votes:
    DisplayBox.Text = "Found " + GetVoteCount(user) + " recent votes";
  case Category.Videos:
    DisplayBox.Text = "Found " + GetVideoCount(user) + " submitted videos";

It’s pretty ‘wordy’ for a start, and crucially we are duplicating the DisplayBox.Text = bit 5 times which is not ideal. Wouldn’t it be nice to make the code shorter, clearer and better? It is really almost too easy! Define a new typed dictionary with Category as a key and a Func<> as the value:

var categoryMap = new Dictionary<Category, Func<User, string>>
  { Category.Articles, u => "There are " + GetArticleCount(u) + " articles"},
  { Category.Posts, u => "There are " + GetPostCount(u) + " posts" },
  { Category.Comments, u => "There is " + GetCommentCount(u) +
                      " comments on " + GetPostCount(u) + " posts" },
  { Category.Votes, u => "Found " + GetVoteCount(u) + " recent votes" },
  { Category.Videos, u => "Found " + GetVideoCount(u) + " submitted videos" }

The Func<User, string> declaration defines an inline method taking a single User argument and returning a string. All we then need to do is check we have a matching Category key in the map and then execute the matching function:

if (categoryMap.ContainsKey(category))
  DisplayBox.Text = categoryMap[category](user);

This is overall more than a third less lines, and your intent is more clearly described.

Update: Dave Van den Eynde pointed out the issue of the overhead involved setting up a dictionary. I ran some tests, which you can read about in the comments, the result being there is a slight overhead using this technique (0.003ish of a millisecond) when run a single time. If this code exists in a loop however, define the dictionary outside of your loop and it can actually be very slightly faster (1 millisecond in 10,000 repetitions) than using switch. I thought it was worth pointing out the pros and cons here for those who don't read comments.

Happy coding!