In C#, how often do you use #region? Lately, I find myself using them only because "I should".
For the most part, I think #region indicates the need for refactoring. Other times, I use #region to hide all my private fields or something similar. Usually, there are so few of these per class that it's unneeded (but it looks nice?). In the end, it's probably more trouble opening and closing them when I need to add new fields.
There are times that a #region makes sense. If you have repeating code, that cannot be refactored, a #region with a short description can be quite nice. See Accessing Private Members in C# for an example. This is rare though, always look for refactoring before settling on a #region. Also, in .NET 1.1 #region is great around generated code. However, in .NET 2.0, with the introduction of partial classes there seems to be less and less need for #region.