Can I upgrade to latest Drush? Or will that break Aegir?

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I've been getting mixed messages as I read the docs, discussions, the google, etc. Does Aegir require Drush 4.5? I've read that it wouldn't work with Drush 5, but that could be old news??

Currently, if I run 'drush pm-update' I get thrown the endless error: "strpos(): Empty delimiter pm.drush.inc:1131"

I've read this is drush bug and the solution is to upgrade drush, but I've also read that Aegir cannot run anything above Drush 4.5.

If I run 'drush dl drush' I get asked if I'd like to back up my current 4.5 version and install the 5.8 version, very considerate of my Ubuntu 11.10 server, and I'm tempted to simply choose 'y' and see... but then if Aegir couldn't run with anything above 4.5, I'd have a bunch of work figuring out how to downgrade drush to the older version...

Thanks