Besides DAR not working if the backup was done pre-FP3 (as the information 
is not available in the catalog):

DAR will not work if there is any wildcard in the restore.
DAR will not work if you ask for a folder name, rather than individual 
files.
DAR will not work if you request > 1024 files restored.

When it does not work, as a rule of thumb it takes as long for the restore 
to complete as the backup took.  However, the files you request may 
actually be restored much sooner - it is just that NBU has to read all 
through all the tapes, to see if there might be anything else on there 
that matches the request.  So keep and eye on  the restore-to area, and 
you may be able to kill the job if you get back what you want sooner.

You can avoid these if you:

1.      If you use the GUI, hunt-and-peck for every file, not the folders.
2.      Use bplist to get a list of the files that match the restore 
request.  Process the output (e.g. with AWK) to pre-pend the length of the 
file path to each line, and feed that as a file selection list to 
bprestore.  Don't forget to split into jobs of < 1024 files.  Well the 
theory is OK, I can't see it being practical for most operators to do.

You can always look at the logs as they say if DAR is being turned off. 
Not sure what verbosity you need.

When DAR works, it takes 3-5 minutes for us to restore.  When it does not, 
it takes maybe 15 hours.

William D L Brown