C#

bool attached = false;
Point oldPos;

private void button1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
	attached = true;
	oldPos = button1.PointToScreen(new Point(e.X, e.Y));
}

private void button1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
	Move(button1.PointToScreen(new Point(e.X, e.Y)));
}

private void button1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
{
	attached = false;
}

private void Form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
	Move(PointToScreen(new Point(e.X, e.Y)));
}

private void Move(Point p) 
{
	if (attached) 
	{
		button1.Left -= oldPos.X - p.X;
		button1.Top -= oldPos.Y - p.Y;
		oldPos = p;
	}
}

const int bufferSize = 4096;
byte[] buffer = new byte[bufferSize];

int readBytes;
while ((readBytes = src.Read(buffer, 0, buffer.Length)) != 0)
{
    dest.Write(buffer, 0, readBytes);
}