Upgrading using streaming replication

Hi there,

I have done quite a bit of searching but have been unable to find any
way to do this. I am quite keen to use PostgreSQL 9.0's streaming
replication to create a master/slave write/read setup. However I am
unsure of an upgrade procedure whilst using streaming replication that
doesn't yield any downtime (including being able to write). From what
I have read the WAL won't be compatible between 9.0 and 9.1 so it
won't be possible to take the slave off-line and upgrade it, promote
it to master and then upgrade the old master.

So I was wondering if anyone knows of a method that allows you to do
this. Sorry if this is an often asked question and I just haven't been
able to find the answer.

Regards,
Damien