I used peslink to link data from excel to powerpoint, but when I changed the data in excel it didn't update in my presentation.  Closing and reopening the powerpoint didn't help either.  I thought preslink linked the data?

In PowerPoint, click PresLink | Linked Items.  You can hit Select All, then Update. 

Or right click & say Update. 

PresLink is designed to update linked data only when specifically requested.  This prevents accidental or unwanted changes to data in Word documents or PowerPoint presentations.  But we've made it easy to update all the links in a document.  The method described above (Select All, Update) is a quick way to accomplish this. 

Or you could choose "Linked Items" from the PresLink menu, which will display the Linked Items dialog, and click the Select All and Update buttons to update all your links.