diff --git a/cmd/shared.go b/cmd/shared.go
index 865f74115..267ab4118 100644
--- a/cmd/shared.go
+++ b/cmd/shared.go
@@ -172,7 +172,7 @@ func apply(cmd *cobra.Command, args []string, existing string, opts applyOptions
 				// TODO: we want richer diagnostics in the event that a plan apply fails.  For instance, we want to
 				//     know precisely what step failed, we want to know whether it was catastrophic, etc.  We also
 				//     probably want to plumb diag.Sink through apply so it can issue its own rich diagnostics.
-				result.C.Diag().Errorf(errors.ErrorPlanApplyFailed, err)
+				sink().Errorf(errors.ErrorPlanApplyFailed, err)
 			}
 
 			// Print out the total number of steps performed (and their kinds), if any succeeded.
@@ -201,6 +201,7 @@ func apply(cmd *cobra.Command, args []string, existing string, opts applyOptions
 			fmt.Printf(colors.Colorize(s))
 
 			// Now save the updated snapshot to the specified output file, if any, or the standard location otherwise.
+			// TODO: perform partial updates if we weren't able to perform the entire planned set of operations.
 			if opts.Delete {
 				contract.Assert(result.Mugfile != "")
 				deleteSnapshot(result.Mugfile)
@@ -223,7 +224,7 @@ func applyExisting(cmd *cobra.Command, args []string, opts applyOptions) {
 	// Read in the snapshot argument.
 	// TODO: if not supplied, auto-detect the current one.
 	if len(args) == 0 {
-		fmt.Fprintf(os.Stderr, "fatal: missing required snapshot argument")
+		fmt.Fprintf(os.Stderr, "fatal: missing required snapshot argument\n")
 		os.Exit(-1)
 	}
 
diff --git a/pkg/resource/plan.go b/pkg/resource/plan.go
index 85223d379..fbdaeef99 100644
--- a/pkg/resource/plan.go
+++ b/pkg/resource/plan.go
@@ -193,17 +193,19 @@ func (s *step) Apply() (error, ResourceState) {
 	// Now simply perform the operation of the right kind.
 	switch s.op {
 	case OpCreate:
+		contract.Assertf(!s.res.HasID(), "Resources being created must not have IDs already")
 		id, err, rst := prov.Create(s.res)
 		if err != nil {
 			return err, rst
 		}
 		s.res.SetID(id)
 	case OpDelete:
-		contract.Assertf(string(s.res.ID()) == "", "Expected resource to be created has no ID")
+		contract.Assertf(s.res.HasID(), "Resources being deleted must have IDs")
 		if err, rst := prov.Delete(s.res); err != nil {
 			return err, rst
 		}
 	case OpUpdate:
+		contract.Assertf(s.res.HasID(), "Resources being updated must have IDs")
 		id, err, rst := prov.Update(s.res, s.old)
 		if err != nil {
 			return err, rst
diff --git a/pkg/resource/plugin.go b/pkg/resource/plugin.go
index b3860d491..34ea18962 100644
--- a/pkg/resource/plugin.go
+++ b/pkg/resource/plugin.go
@@ -188,8 +188,8 @@ func (p *Plugin) Read(id ID, t tokens.Type) (PropertyMap, error) {
 // Update updates an existing resource with new values.  Only those values in the provided property bag are updated
 // to new values.  The resource ID is returned and may be different if the resource had to be recreated.
 func (p *Plugin) Update(old Resource, new Resource) (ID, error, ResourceState) {
-	contract.Requiref(old.ID() != "", "old.ID", "not empty")
-	contract.Requiref(new.ID() != "", "old.ID", "not empty")
+	contract.Requiref(old.HasID(), "old.ID", "not empty")
+	contract.Requiref(new.HasID(), "old.ID", "not empty")
 	contract.Requiref(old.ID() == new.ID(), "old.ID, new.ID", "==")
 	contract.Requiref(old.Type() != "", "old.Type", "not empty")
 	contract.Requiref(new.Type() != "", "new.Type", "not empty")
@@ -220,7 +220,7 @@ func (p *Plugin) Update(old Resource, new Resource) (ID, error, ResourceState) {
 
 // Delete tears down an existing resource.
 func (p *Plugin) Delete(res Resource) (error, ResourceState) {
-	contract.Requiref(res.ID() != "", "res.ID", "not empty")
+	contract.Requiref(res.HasID(), "res.ID", "not empty")
 	contract.Requiref(res.Type() != "", "res.Type", "not empty")
 
 	id := string(res.ID())
diff --git a/pkg/resource/resource.go b/pkg/resource/resource.go
index 3f598477a..7914ccab1 100644
--- a/pkg/resource/resource.go
+++ b/pkg/resource/resource.go
@@ -25,6 +25,7 @@ type Resource interface {
 	Moniker() Moniker        // the resource's object moniker, a human-friendly, unique name for the resource.
 	Type() tokens.Type       // the resource's type.
 	Properties() PropertyMap // the resource's property map.
+	HasID() bool             // returns true if the resource has been assigned an ID.
 	SetID(id ID)             // assignes an ID to this resource, for those under creation.
 }
 
@@ -52,8 +53,9 @@ func (r *resource) Moniker() Moniker        { return r.moniker }
 func (r *resource) Type() tokens.Type       { return r.t }
 func (r *resource) Properties() PropertyMap { return r.properties }
 
+func (r *resource) HasID() bool { return (string(r.id) != "") }
 func (r *resource) SetID(id ID) {
-	contract.Requiref(string(r.id) == "", "id", "empty")
+	contract.Requiref(!r.HasID(), "id", "empty")
 	r.id = id
 }