[9.0] hot standby plus streaming replication questions

Hi list,
I'm trying the new features into a test environment for see how all
works and I'm finding first problems with setup.

After reading the various Streaming_Replication, Warm_Standby and
What's_new_in_PostgreSQL_9.0 on the wiki, one first question born: both
server (master and standby) need a common directory where read and write
the wal files? I don't find a reference where it's specified or said.
On my tests it's needed only for the first startup of the standby
server. After I can disable it on the master (archive_mode=off) and the
replication is
performed however, although the client warn me about a "no such file or
directory wal_archive/00000001000000000000000N+1" where N is the last
file wal archive that I have on the master, before disable the
"archive_mode".
Also on the my tests, I see that the replication happen also if I stop
the slave, add a 1k records to the master and re-start the slave. After
some seconds, on the master I see the connection and querying the slave
I see that all the record (previous inserted on the master) are there!

Just another question about replication: there is the possibility to
build a sync between a 32 and a 64 bit (on linux)?

Thanks,
Michele