-- 11/29/2011 UPDATE --
Thanks to Falk and Furiant for the comments and troubleshooting. I've added an extra step to account for situations where users have read-only permissions. The corev4.css style sheet does not get loaded by default on minimal.master for these users and therefore does not style the navigation properly.
John Ross from SharePoint 911 has an article that describes why SP2010 search center templates use minimal.master for their master pages.
One of the most frequent requests I get from users that have (fairly) vanilla SP2010 deployments is to have the global navigation links included on search pages. The simplest way to do this is to make a copy of minimal.master and copy a div tag from v4.master. Here are the steps:
1. Open SharePoint Designer and connect to the root of the site collection where your search center lives. You’re going to need to access to the master page gallery.
2. Select “Master Pages” from the “Site Objects” pane on the left.
3. Make a copy of “minimal.master” and name it something nice like “search.master”. Open this new master page in split view.
4. Find the div tag that encloses the “PlaceHolderTitleBreadcrumb” content place holder control and paste in this markup (which I just copied out of v4.master) right above it.
<div class="s4-lp s4-toplinks">
<asp:ContentPlaceHolder id="PlaceHolderTopNavBar" runat="server">
<asp:ContentPlaceHolder id="PlaceHolderHorizontalNav" runat="server">
<SharePoint:AspMenu
ID="TopNavigationMenuV4"
Runat="server"
EnableViewState="false"
DataSourceID="topSiteMap"
AccessKey="<%$Resources:wss,navigation_accesskey%>"
UseSimpleRendering="true"
UseSeparateCss="false"
Orientation="Horizontal"
StaticDisplayLevels="2"
MaximumDynamicDisplayLevels="1"
SkipLinkText=""
CssClass="s4-tn"/>
<SharePoint:DelegateControl runat="server"
ControlId="TopNavigationDataSource" Id="topNavigationDelegate">
<Template_Controls>
<asp:SiteMapDataSource
ShowStartingNode="False"
SiteMapProvider="SPNavigationProvider"
id="topSiteMap"
runat="server"
StartingNodeUrl="sid:1002"/>
</Template_Controls>
</SharePoint:DelegateControl>
</asp:ContentPlaceHolder>
</asp:ContentPlaceHolder>
</div>
5. Find the CSS registration tag for minimalv4.css and paste in this tag right above it.
<SharePoint:CssRegistration Name="corev4.css" runat="server"/>
6. Save, check in, and publish the new master page.
7. Browse to your search center and change the site master page to use the one you just published. Your global navigation should now show up directly below the dark blue band that has the site logo and title.
