SharePoint 2010 Linked Data Source item link field

For Direct Page:

<a href="{@FileDirRef}/DispForm.aspx?ID={@ID}" ONCLICK="GoToLink(this);return false;"><xsl:value-of select="@Title" /></a>

For Popup:

<a href="javascript:OpenPopUpPage('{@FileDirRef}/DispForm.aspx?ID={@ID}');"><xsl:value-of select="@Title"/></a>

How to cancel all existing Work Flows on an item

 // Terminate all existing In-Progress workflows.

 foreach (SPWorkflow workflow in item.Workflows)
 {
   SPWorkflowManager.CancelWorkflow(workflow);
 }

SharePoint 2010 Workflow cannot compare multiple Person filed

Please note that if the person field is only single user field. The comparison seems to be working. If you want you can write a custom activity to do that.

how to turn on developer dashboard

Using STSADM

Open a command window to the %ProgramFiles%\Common Files\Microsoft Shared Debug\Web Server Extensions\14\BIN directory and enter one of the following commands, depending on the desired display mode.

Mode	Command
On	stsadm -o setproperty -pn developer-dashboard -pv on
OnDemand	stsadm -o setproperty -pn developer-dashboard -pv ondemand

REF:
http://msdn.microsoft.com/en-us/library/ff512745(v=office.14).aspx

How to open SharePoint Page in WebPart Maintenance Mode

Maintenance page can be opened by adding the following query string to the page URL

?contents=1