C#

using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;

namespace TestVisibleLog
{
    public class VisibleLog : RichTextBox
    {
        private string timeStampFmt;
        private int maximumBytes;
        private string[] timeStampTokens;
        private BackgroundWorker AddEntryInBackground;

        public VisibleLog ( )
        {
            this.Enabled = false; // must be set to true by the controlling process.

            timeStampFmt = "";
            maximumBytes = 512;
            timeStampTokens = "dow,yoc,moy,dom,hh,mm,ss".Split(',');

            this.Text = "";

            // Create a background worker that will be responsible for updating the control's text with entries from
            // any thread.
            AddEntryInBackground = new System.ComponentModel.BackgroundWorker();
            // Add the event handler to be called when the the background worker has an entry to add.
            AddEntryInBackground.DoWork += new System.ComponentModel.DoWorkEventHandler(AddEntryInBackground_DoWork);
            // Add the event hander to be called after the background work has been done.
            AddEntryInBackground.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(AddEntryInBackground_RunWorkerCompleted);

        }

        public string TimeStampFormat
        {
            set
            {
                timeStampFmt = value;
                if ( value != "" )
                {
                    timeStampFmt += ": ";
                    for ( int index = 0; index < timeStampTokens.Length; index++ )
                        timeStampFmt = timeStampFmt.Replace(timeStampTokens[index], "{" + index.ToString() + "}");
                }
            }
        }

        public int MaxBytes
        {
            set
            {
                maximumBytes = value;
            }
        }

        public void AddEntry ( string EntryText )
        {
            // Get the background worker to handle putting the entry in the form.  EntryText will be passed
            // AddEntryInBackground's DoWork event;
            while ( AddEntryInBackground.IsBusy )
                Thread.Sleep(100);
            AddEntryInBackground.RunWorkerAsync(EntryText);
        }

        private void AddEntryInBackground_DoWork ( object sender, DoWorkEventArgs e )
        {
            string entryFormat = timeStampFmt + "{" + (timeStampTokens.Length).ToString() + "}.";
            string logEntry = string.Format(entryFormat,
                            DateTime.Now.DayOfWeek.ToString().Substring(0, 3),
                            (DateTime.Now.Year % 100).ToString("D2"),
                            DateTime.Now.Month.ToString("D2"),
                            DateTime.Now.Day.ToString("D2"),
                            DateTime.Now.Hour.ToString("D2"),
                            DateTime.Now.Minute.ToString("D2"),
                            DateTime.Now.Second.ToString("D2"),
                            e.Argument);
            // Contrary to the name of this method, the actual AddEntry work is not done here.  Instead
            // the text to be added to the log is placed in the DoWorkEventArgs to be picked up by the
            // RunWorkerCompleted event.
            e.Result = logEntry;
        }

        private void AddEntryInBackground_RunWorkerCompleted ( object sender, RunWorkerCompletedEventArgs e )
        {
            int overage = this.Text.Length + ((string)(e.Result)).Length + 1 - maximumBytes;
            if ( overage > 0 )
            {
                int cutoff = this.Text.IndexOf("\n", overage);
                if ( cutoff == -1 )
                    this.Text = (string)e.Result;
                else
                    this.Text = this.Text.Substring(cutoff + 1) + "\n" + (string)e.Result;
            }
            else
                this.Text += ((this.Text.Length > 0) ? "\n" : "") + (string)e.Result;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

namespace TestVisibleLog
{
    public class Form1 : Form
    {
        public Form1 ( )
        {
            InitializeComponent();

            this.statusLogBox.TimeStampFormat = "yoc/moy/dom-hh:mm:ss - ";
            this.statusLogBox.AddEntry("This is entry 1");
            System.Threading.Thread.Sleep(60000);
            this.statusLogBox.AddEntry("And here is another entry");
        }

        private System.ComponentModel.IContainer components = null;
        private VisibleLog statusLogBox;

        protected override void Dispose ( bool disposing )
        {
            if ( disposing && (components != null) )
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        private void InitializeComponent ( )
        {
            this.components = new System.ComponentModel.Container();
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.Text = "Form1";
            statusLogBox = new VisibleLog();
            this.SuspendLayout();
            this.statusLogBox.Location = new System.Drawing.Point(13, 13);
            this.statusLogBox.Name = "statusLogBox";
            this.statusLogBox.ReadOnly = true;
            this.statusLogBox.ScrollBars = System.Windows.Forms.RichTextBoxScrollBars.Both;
            this.statusLogBox.Size = new System.Drawing.Size(256, 241);
            this.statusLogBox.TabIndex = 0;
            this.statusLogBox.Text = "";
            this.statusLogBox.Anchor = AnchorStyles.Bottom | AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Right;
            this.statusLogBox.Enabled = true;
            this.Controls.Add(statusLogBox);
            this.ResumeLayout();
        }
    }

    static class Program
    {
        [STAThread]
        static void Main ( )
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

string xmlString = myXDocument.Declaration.ToString() + myXDocument.ToString(SaveOptions.DisableFormatting);