Creating shapefile from current dataframe extents in layout view of ArcMap?

I created a tool to do this via a Toolbox in ArcGIS 10. It might be easier to use than scripting. You can download from https://github.com/nickpeihl/mapindextool. Just copy your mxd(s) into a folder and run the tool on that folder. It will create a shapefile containing all the main extents of each mxd in that folder.

This c# code could be used to build an add-in for Arcmap.

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Windows.Forms;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.Carto;
using ESRI.ArcGIS.ArcMapUI;
using ESRI.ArcGIS.DataSourcesFile;
using ESRI.ArcGIS.Geodatabase;

namespace MainToolsAddin
{
    public class Extent2ShapefileButton : ESRI.ArcGIS.Desktop.AddIns.Button
    {
        public Extent2ShapefileButton()
        {
        }

        protected override void OnClick()
        {
            try
            {
                var polygon = GetExtentPolygon(ArcMap.Document.FocusMap);
                //IGraphicsContainer gc = ArcMap.Document.FocusMap as IGraphicsContainer;
                //var element = new PolygonElementClass() as IElement;
                //element.Geometry = polygon;
                //((IFillShapeElement)element).Symbol = ((IDocumentDefaultSymbols)ArcMap.Document).FillSymbol;
                //gc.AddElement(element,0);
                //((IActiveView)ArcMap.Document.FocusMap).Refresh();
                WritePolygon(@"C:\projects\forums\extents.shp", polygon);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        protected override void OnUpdate()
        {
        }

        private void WritePolygon(string shpFilePath, IGeometry geom)
        {
            var featClass = OpenShapeFile(shpFilePath);
            if (featClass == null)
                featClass = CreateShapeFile(shpFilePath, geom);
            IFeature feat = featClass.CreateFeature();
            feat.Shape = geom;
            feat.Store();
        }
        private IFeatureClass CreateShapeFile(string shpFilepath, IGeometry geom)
        {
            System.IO.FileInfo fi = new FileInfo(shpFilepath);
            var wsf = Activator.CreateInstance(Type.GetTypeFromProgID("esriDataSourcesFile.ShapefileWorkspaceFactory")) as IWorkspaceFactory;
            var fws = wsf.OpenFromFile(fi.DirectoryName, 0) as IFeatureWorkspace;
            IFieldsEdit flds = new FieldsClass();
            flds.AddField(MakeField("ObjectID", esriFieldType.esriFieldTypeOID,0));
            IGeometryDefEdit geomDef = new GeometryDefClass();
            geomDef.GeometryType_2 = geom.GeometryType;
            geomDef.SpatialReference_2 = geom.SpatialReference;
            var shpField = MakeField("Shape", esriFieldType.esriFieldTypeGeometry, 0) as IFieldEdit;
            shpField.GeometryDef_2 = geomDef;
            flds.AddField(shpField);
            flds.AddField(MakeField("Name", esriFieldType.esriFieldTypeString, 16));
            string fcName = fi.Name;
            if (fcName.ToUpper().EndsWith(".SHP"))
                fcName = fcName.Substring(0, fcName.LastIndexOf("."));

            var fc = fws.CreateFeatureClass(fcName, flds, null, null, esriFeatureType.esriFTSimple, "Shape", "");
            return fc;
        }

        private IField MakeField(string name, esriFieldType fType, int length)
        {
            IFieldEdit fld = new FieldClass();
            fld.Name_2 = name;
            fld.Type_2 = fType;
            if (length > 0 && fType == esriFieldType.esriFieldTypeString)
                fld.Length_2 = length;
            return fld;
        }

        private IFeatureClass OpenShapeFile(string shpFilepath)
        {
            var wsf = Activator.CreateInstance(Type.GetTypeFromProgID("esriDataSourcesFile.ShapefileWorkspaceFactory")) as IWorkspaceFactory;

            System.IO.FileInfo fi = new FileInfo(shpFilepath);
            string name = fi.Name.ToUpper().EndsWith(".SHP") ? fi.Name.Substring(0, fi.Name.LastIndexOf(".")) : fi.Name;
            string fileName = String.Format("{0}.shp", name);
            if (File.Exists(System.IO.Path.Combine(fi.DirectoryName,fileName)))
            {
                var fws = wsf.OpenFromFile(fi.DirectoryName, 0) as IFeatureWorkspace;
                return fws.OpenFeatureClass(name);
            }
            else
                return null;
        }

        private IPolygon GetExtentPolygon(IMap map)
        {
            // A polygon is returned since the dataframe might be rotated
            var grphCont = ArcMap.Document.PageLayout as IGraphicsContainer;
            var mapFrame = grphCont.FindFrame(map) as IMapFrame;
            var av = map as IActiveView;
            var extent = mapFrame.MapBounds.Envelope;
            ISegmentCollection sc = new PolygonClass() as ISegmentCollection;
            sc.SetRectangle(extent);

            var center = ((IArea)extent).Centroid;
            var angle = -(av.ScreenDisplay.DisplayTransformation.Rotation / 180.0 * Math.PI);
            ((ITransform2D)sc).Rotate(center, angle);
            return (IPolygon)sc;                        
        }
    }
}

When you create a new add-in project with Visual Studio, you should see some options like this. I'm not sure if it works with Visual Studio Express, or whether the ArcObjects SDK needs to be installed.

Here is a basic python script to create a polygon from the dataframe extent. Adjust the variable to suit your needs. If you just want a simple extent polygon, you can get rid of 'feat', 'scale', and 'Page'. ('Page' will only work if you are using data driven pages).

doc = arcpy.mapping.MapDocument("current")
df = arcpy.mapping.ListDataFrames(doc)[0] #First Dataframe
extent = df.extent
fc = arcpy.GetParameterAsText(0)
feat = arcpy.GetParameterAsText(1)
scale = arcpy.GetParameterAsText(2)
Page = doc.dataDrivenPages.currentPageID

# Create Extent Polygon
array = arcpy.Array()
array.add(extent.lowerLeft)
array.add(extent.lowerRight)
array.add(extent.upperRight)
array.add(extent.upperLeft)
array.add(extent.lowerLeft)
polygon = arcpy.Polygon(array)
cursor = arcpy.da.InsertCursor(fc,["SHAPE@","Page","Feature","Scale"])
cursor.insertRow([polygon, Page, feat, scale])
del cursor