*.dwp and *.webpart confusion about Web Part implementation and usage in SharePoint

Recently I was really confused about which type of web part deployment file extension I should use. After some research I figured the following out (which might be interesting for all SharePoint newbies):

• .dwp is a web part description xml file used prior and up to SharePoint 2007/2010, therefore is still supported
• .webpart is the newer extension which came with MOSS 2007

So whats the true difference:
.DWP:
It uses the following namespace xmlns=http://schemas.microsoft.com/WebPart/v2 by default.
The markup looks something like:

<?xml version="1.0"?>
<WebPart xmlns="http://schemas.microsoft.com/WebPart/v2">
   <Assembly>AssemblyName(with no .dll extension), 
      Version=VersionNumber, Culture=Culture, 
      PublicKeyToken=PublicKeyToken</Assembly>
   <TypeName>WebPartNamespace.WebPartClassName</TypeName>
   <Title>DefaultWebPartTitle</Title>
   <Description>WebPartDescription</Description>
</WebPart> 

Also interesting is that if you derive your web part from Microsoft.SharePoint.WebPartPages.WebPart and switch to your web part gallery and select "New", you will see a list of all registered DLLs that contain web parts, SharePoint suggests the dwp file extension.

SharePoint automatically suggests the type of the web part description file extension, either *.webpart or *.dwp.

- Microsoft.SharePoint.WebPartPages.WebPart = *.dwp

- System.Web.UI.WebControls.WebParts.WebPart = *.webpart

.WEBPART

It uses the following namespace by default: xmlns="http://schemas.microsoft.com/WebPart/v3"

The example markup for it:

<?xml version="1.0" encoding="utf-8"?>
<webParts>
  <webPart xmlns="http://schemas.microsoft.com/WebPart/v3">
    <metaData>
      <!--
      The following Guid is used as a reference to the web part class, 
      and it will be automatically replaced with actual type name at deployment time.
      -->
      <type name="My.SharePoint.SomeIntegration.SomeIntegrationWebPart, My.SharePoint.SomeIntegration, Version=1.0.0.0, Culture=neutral, PublicKeyToken=3066ecdd584a19bd" />
      <importErrorMessage>Cannot import SomeIntegration Web Part.</importErrorMessage>
    </metaData>
    <data>
      <properties>
        <property name="Title" type="string">Some Integration Web Part</property>
        <property name="Description" type="string">The web part shows a document type/category tree and an item list.</property>
        <property name="CacheDuration" type="int">5</property>
        <property name="SomeListName" type="string">http://mossdev/Lists/Some%20Import%20List</property>
        <property name="RootName" type="string">Document Type</property>
        <property name="ChromeState" type="chromestate">Normal</property>
        <property name="ChromeType" type="chrometype">None</property>
      </properties>
    </data>
  </webPart>
</webParts>

What happens if you try to add a SharePoint web part to a web part zone which was deployed to SharePoint with a *.webpart file is that you will get a nice popup error message:
Incompatible Web Part markup detected. Use *.dwp web part XML instead of *.webpart web part xml.

I hope this will help you to understand SharePoint web part development and deployment a little better.