If you're using AutoCAD 2005 or 2006 you may have noticed the great AutoCAD Fields. Fields are a really nice addition that give you quick access to various types of information via TEXT, MTEXT or an Attribute. Much easier than the old school (express tool RTEXT). Now many believe that AutoCAD Fields DO NOT work in Xref's. But fact is that they do, well some do. If you're trying to use an AutoCAD Field in an Xref, you're probably trying to use in you're title sheet. And most the Fields that pertain to title sheets work in XREF's. So you can access the Author, DWG Name, and Date Field all from inside you're Xref. Most the others however, you wont be able to access from your XREF.
Another little trick I use with fields is copying fields to other Attribute objects. If you want to copy your field to another attribute. All you need to do is enter the attribute by using a command such as DDEDIT, then click on the field you want to copy to enter the Field dialog box. Now you're field you clicked on will be already highlighted in the Field dialog box. At the bottom of the Dialog box you'll see a Field Expression with a bunch of charters like %<AcVar .......>%. Simply highlight the whole string, right click and copy this to your clipboard. Now, just go back to your attribute dialog box or Mtext editor, right click, and paste away to all the locations you want. Simple, but pretty fast if you're working with many types of Fields in you're drawings.