It can be a little tedious to verify replication status in a large Active Directory environment via the Sites and Services snap-in.  Here is a command I use quite frequently to check the replication status of all domain controllers:
REPADMIN /SHOWREPL * /CSV >showrepl.csv
View the file in Microsoft Excel and perform the following filtering options to get a good quick overview of replication health:
1. Hide columns A and B
2. Select the row just under Column headers and choose Window / Freeze Pane (In Excel 2007: View tab, Window, Freeze Panes, Freeze Top Row)
3. Highlight the entire spreadsheet and choose Data / Filter / Auto-Filter
4. Click on the down-arrow for the "Last Failure Status" column, and choose "does not
equal" then type in "0"  (In Excel 2007: Uncheck the box next to "0")
You are left with a list of domain controllers having replication problems.  From a cmd prompt, use:
"net helpmsg ErrorCodeNumber" to identify the replication error
(eg. net helpmsg 1396)
 ShowrepCSV