Pet Peeve: Not «using» IDisposable

I am amazed that I see very little usage of the using statement in c# code.  This is a nobrainer for clean code, but continually I see people rolling their own try catch blocks around candidates for using statements.

Take the System.Data.SqlConnection for example.   I constantly see alot of the following style of coding:

string connectionString = "your connection string";
SqlConnection cn = null;
SqlDataAdapter da = null;
DataTable dt = new DataTable();

try{
  cn = new SqlConnection(connectionString);
  da = new SqlDataAdapter("select * from sometable", cn);
  da.Fill(dt);
}finally{
  if(cn != null){
    cn.Close();
  }
}

string connectionString = "your connection string";
DataTable dt = new DataTable();
using (SqlConnection cn = new SqlConnection(connectionString))
using (SqlDataAdapter da = new SqlDataAdapter("select * from sometable", cn)){
  da.Fill(dt);
}

  .try
  {
    IL0014:  ldstr      "select * from sometable"
    IL0019:  ldloc.2
    IL001a:  newobj     instance void [System.Data]System.Data.SqlClient.SqlDataAdapter::.ctor(string,
                                                                                                class [System.Data]System.Data.SqlClient.SqlConnection)
    IL001f:  stloc.3
    .try
    {
      IL0020:  nop
      IL0021:  ldloc.3
      IL0022:  ldloc.1
      IL0023:  callvirt   instance int32 [System.Data]System.Data.Common.DbDataAdapter::Fill(class [System.Data]System.Data.DataTable)
      IL0028:  pop
      IL0029:  nop
      IL002a:  leave.s    IL003e
    }  // end .try
    finally
    {
      IL002c:  ldloc.3
      IL002d:  ldnull
      IL002e:  ceq
      IL0030:  stloc.s    CS$4$0000
      IL0032:  ldloc.s    CS$4$0000
      IL0034:  brtrue.s   IL003d
      IL0036:  ldloc.3
      IL0037:  callvirt   instance void [mscorlib]System.IDisposable::Dispose()
      IL003c:  nop
      IL003d:  endfinally
    }  // end handler
    IL003e:  nop
    IL003f:  leave.s    IL0053
  }  // end .try
  finally
  {
    IL0041:  ldloc.2
    IL0042:  ldnull
    IL0043:  ceq
    IL0045:  stloc.s    CS$4$0000
    IL0047:  ldloc.s    CS$4$0000
    IL0049:  brtrue.s   IL0052
    IL004b:  ldloc.2
    IL004c:  callvirt   instance void [mscorlib]System.IDisposable::Dispose()
    IL0051:  nop
    IL0052:  endfinally
  }  // end handler

This is taken from the MS docs on SqlConnection:To ensure that connections are always closed, open the connection inside of a using block, as shown in the following code fragment. Doing so ensures that the connection is automatically closed when the code exits the block.