<form id="Form1" method="post" runat="server">
		<asp:CheckBox Runat=server ID="chkCheck1" Text = "Option 1"/>
		<asp:CheckBox Runat=server ID="chkCheck2" Text = "Option 2"/>
		<asp:CheckBox Runat=server ID="chkCheck3" Text = "Option 3"/>
		<asp:Button Runat=server ID="btnOk" Text="OK"/>
    </form>

public class WebForm1 : System.Web.UI.Page
	{
		private void InitializeComponent()
		{    
			chkCheck1.CheckedChanged += new EventHandler(OnCheckedChanged);
			chkCheck2.CheckedChanged += new EventHandler(OnCheckedChanged);
			chkCheck3.CheckedChanged += new EventHandler(OnCheckedChanged);
			btnOk.Click += new EventHandler(btnOk_Click);
		}
		
		private ArrayList _changedChecks = new ArrayList();

		protected CheckBox chkCheck1;
		protected CheckBox chkCheck2;
		protected CheckBox chkCheck3;
		protected Button btnOk;

		override protected void OnInit(EventArgs e)
		{
			InitializeComponent();
			base.OnInit(e);
		}

		private void OnCheckedChanged(object sender, EventArgs e)
		{
            _changedChecks.Add(sender);
		}

		private void btnOk_Click(object sender, EventArgs e)
		{
			foreach (CheckBox checkBox in _changedChecks)
				Response.Write(checkBox.ID + " was changed");
		}
	}