WordPress MU

The install process is SO easy. As it says, 5 mins and you're done. It's great. What other things would you recommend in terms of modifying configuration settings, or adding essential mods which can't be added later, BEFORE GO LIVE i.e. when all and sundry start creating blogs? What settings can't you change or do you want to make sure are correct from the start... Any lockdown/hardening tips? Or did you just take wpmu out of the box (so to speak). I just want to make any changes that i might need to do before users are using system THANKS

Install widgets and do any theme tweaking. users are going to want to do things to their sidebars.
other than that, most stuff can be done afterwards as needed.

Don't rush it, as exciting as it may be.

Test, test, test.

Be sure you've installed it where you want it. If you installed it in a subdirectory (like domain.tld/blogs), be sure that's where you want it. Usually the root directory seems to be the best overall. especially for using subdomains.

Plus what Andrea said, of course.

as lunabyte mention, i think being sure about your setup is the most important. If you'll want subdomains, get it right now. If you'll want wpmu installed in a subdirectory, get it right now. Things will be more painful later.
OH, and if you target thousands of users, split DBs now, or think about how you wanna scale right away. Much harder and longer to do it once you have tons of blogs up and running.

some very good suggestions and advice, thank you. with regard to the subdirectory/domain debate, I'm going to install wpmu into root of:
http://wpmu.sitedomain.tld

and offer subdirectory blogs as
http://wpmu.sitedomain.tld/user1
http://wpmu.sitedomain.tld/user2

etc. Everyone happy with that or any warnings?
I heard mention that some of the mods are only designed for root installs. This is a root install, in a third level domain.... what are the implications?!

Quentin, can i come back and look splitting databases a bit later, when say I've got a few hundred blogs - or does it need ot be done from the outset?

you can do it later on, but then you need to move your users around, which means you have to write a script to do it, and which means downtime for users while their blogs get moved. If you target just a few hundred that wouldn't be a problem to keep a single DB though.