Exposing user data through javascript on a SharePoint 2010 master page.

master.master

<%@ Register Tagprefix="SPSWC" Namespace="Microsoft.SharePoint.Portal.WebControls" Assembly="Microsoft.SharePoint.Portal, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>

<SPSWC:ProfilePropertyLoader runat="server"/>

<script>
CurrentUser = {
  UserName: '<SPSWC:ProfilePropertyValue PropertyName="UserName" TitleMode="true" runat="server" />',
  FirstName: '<SPSWC:ProfilePropertyValue PropertyName="FirstName" TitleMode="true" runat="server" />',
  Lastname: '<SPSWC:ProfilePropertyValue PropertyName="LastName" TitleMode="true" runat="server" />',
  PictureURL: '<SPSWC:ProfilePropertyValue PropertyName="PictureURL" TitleMode="true" runat="server" />',
  Status: '<SPSWC:ProfilePropertyValue PropertyName="SPS-StatusNotes" TitleMode="true" runat="server" />'
};  
</script>