WAL segment management on a standby

Again, thanks to all to have assisted me with getting the WAL segments to both my standby servers. Everything with that is now working quite well. I do have a related followup 
question, however. On these standby's nothing is built in to manage those WAL segments in the archive directory. Thus, that directory can grow to the point where it fills up the 
disk rather quickly. Any good strategies for dealing with the WAL segments that get put in there. Do I really need them after postgresql has copied them up into the pg_xlog 
directory? If so, how far back should I keep them? Yes, I know about keeping everything between backups. So, if my directory looks like:

00000000300000000C000000A1
00000000300000000C000000A2
00000000300000000C000000A3
00000000300000000C000000A3.backup
00000000300000000C000000A4

Could I safely delete the *A1, *A2, and maybe even the *A3 files?
--
Jay