diff --git a/src/addons/transitions/ReactTransitionGroup.js b/src/addons/transitions/ReactTransitionGroup.js
index 95dea6b752..623838c49f 100644
--- a/src/addons/transitions/ReactTransitionGroup.js
+++ b/src/addons/transitions/ReactTransitionGroup.js
@@ -102,7 +102,12 @@ var ReactTransitionGroup = React.createClass({
   render: function() {
     return this.transferPropsTo(
       this.props.component(
-        null,
+        {
+          transitionName: null,
+          transitionEnter: null,
+          transitionLeave: null,
+          component: null
+        },
         this.renderTransitionableChildren(this.props.children)
       )
     );
diff --git a/src/dom/DOMProperty.js b/src/dom/DOMProperty.js
index 1bded212d9..fa031bb87a 100644
--- a/src/dom/DOMProperty.js
+++ b/src/dom/DOMProperty.js
@@ -82,8 +82,11 @@ var DOMPropertyInjection = {
 
       DOMProperty.isStandardName[propName] = true;
 
+      var lowerCased = propName.toLowerCase();
+      DOMProperty.getPossibleStandardName[lowerCased] = propName;
+
       DOMProperty.getAttributeName[propName] =
-        DOMAttributeNames[propName] || propName.toLowerCase();
+        DOMAttributeNames[propName] || lowerCased;
 
       DOMProperty.getPropertyName[propName] =
         DOMPropertyNames[propName] || propName;
@@ -141,6 +144,13 @@ var DOMProperty = {
    */
   isStandardName: {},
 
+  /**
+   * Mapping from lowercase property names to the properly cased version, used
+   * to warn in the case of missing properties.
+   * @type {Object}
+   */
+  getPossibleStandardName: {},
+
   /**
    * Mapping from normalized names to attribute names that differ. Attribute
    * names are used when rendering markup or with `*Attribute()`.
diff --git a/src/dom/DOMPropertyOperations.js b/src/dom/DOMPropertyOperations.js
index cb5d55ad4c..4d4f6b4385 100644
--- a/src/dom/DOMPropertyOperations.js
+++ b/src/dom/DOMPropertyOperations.js
@@ -28,6 +28,36 @@ var processAttributeNameAndPrefix = memoizeStringOnly(function(name) {
   return escapeTextForBrowser(name) + '="';
 });
 
+if (__DEV__) {
+  var reactProps = {
+    '{owner}': true,
+    children: true,
+    dangerouslySetInnerHTML: true,
+    key: true,
+    ref: true
+  };
+  var warnedProperties = {};
+
+  var warnUnknownProperty = function(name) {
+    if (reactProps[name] || warnedProperties[name]) {
+      return;
+    }
+
+    warnedProperties[name] = true;
+    var message = 'Unknown DOM property ' + name + '.';
+    var lowerCasedName = name.toLowerCase();
+
+    // data-* attributes should be lowercase; suggest the lowercase version
+    var standardName = DOMProperty.isCustomAttribute(lowerCasedName) ?
+      lowerCasedName : DOMProperty.getPossibleStandardName[lowerCasedName];
+    if (standardName != null) {
+      message += ' Did you mean ' + standardName + '?';
+    }
+
+    console.warn(message);
+  };
+}
+
 /**
  * Operations for dealing with DOM properties.
  */
@@ -55,6 +85,9 @@ var DOMPropertyOperations = {
       return processAttributeNameAndPrefix(name) +
         escapeTextForBrowser(value) + '"';
     } else {
+      if (__DEV__) {
+        warnUnknownProperty(name);
+      }
       return null;
     }
   },
@@ -85,6 +118,10 @@ var DOMPropertyOperations = {
       }
     } else if (DOMProperty.isCustomAttribute(name)) {
       node.setAttribute(name, value);
+    } else {
+      if (__DEV__) {
+        warnUnknownProperty(name);
+      }
     }
   },
 
@@ -110,6 +147,8 @@ var DOMPropertyOperations = {
       }
     } else if (DOMProperty.isCustomAttribute(name)) {
       node.removeAttribute(name);
+    } else if (__DEV__) {
+      warnUnknownProperty(name);
     }
   }
 
diff --git a/src/dom/__tests__/DOMPropertyOperations-test.js b/src/dom/__tests__/DOMPropertyOperations-test.js
index acc10d6074..ec28cfa970 100644
--- a/src/dom/__tests__/DOMPropertyOperations-test.js
+++ b/src/dom/__tests__/DOMPropertyOperations-test.js
@@ -58,6 +58,16 @@ describe('DOMPropertyOperations', function() {
       )).toBe('id="simple"');
     });
 
+    it('should warn about incorrect casing', function() {
+      spyOn(console, 'warn');
+      expect(DOMPropertyOperations.createMarkupForProperty(
+        'tabindex',
+        '1'
+      )).toBe(null);
+      expect(console.warn.argsForCall.length).toBe(1);
+      expect(console.warn.argsForCall[0][0]).toContain('tabIndex');
+    });
+
     it('should create markup for boolean properties', function() {
       expect(DOMPropertyOperations.createMarkupForProperty(
         'checked',
@@ -141,18 +151,24 @@ describe('DOMPropertyOperations', function() {
 
   describe('injectDOMPropertyConfig', function() {
     it('should support custom attributes', function() {
+      spyOn(console, 'warn');
+
       // foobar does not exist yet
       expect(DOMPropertyOperations.createMarkupForProperty(
         'foobar',
         'simple'
       )).toBe(null);
 
+      expect(console.warn.argsForCall.length).toBe(1);
+
       // foo-* does not exist yet
       expect(DOMPropertyOperations.createMarkupForProperty(
         'foo-xyz',
         'simple'
       )).toBe(null);
 
+      expect(console.warn.argsForCall.length).toBe(2);
+
       // inject foobar DOM property
       DOMProperty.injection.injectDOMPropertyConfig({
         isCustomAttribute: function(name) {
diff --git a/src/dom/components/ReactDOMInput.js b/src/dom/components/ReactDOMInput.js
index 924a5768ae..85b2f33248 100644
--- a/src/dom/components/ReactDOMInput.js
+++ b/src/dom/components/ReactDOMInput.js
@@ -61,6 +61,8 @@ var ReactDOMInput = ReactCompositeComponent.createClass({
     // Clone `this.props` so we don't mutate the input.
     var props = merge(this.props);
 
+    props.defaultChecked = null;
+    props.defaultValue = null;
     props.checked =
       this.props.checked != null ? this.props.checked : this.state.checked;
     // Cast `this.props.value` to a string so equality checks pass.
diff --git a/src/dom/components/ReactDOMTextarea.js b/src/dom/components/ReactDOMTextarea.js
index 4682d74355..78db712093 100644
--- a/src/dom/components/ReactDOMTextarea.js
+++ b/src/dom/components/ReactDOMTextarea.js
@@ -102,6 +102,7 @@ var ReactDOMTextarea = ReactCompositeComponent.createClass({
       '`dangerouslySetInnerHTML` does not make sense on <textarea>.'
     );
 
+    props.defaultValue = null;
     props.value =
       this.props.value != null ? this.props.value : this.state.value;
     props.onChange = this._handleChange;