The latest machine was our mail server. It's a complicated beast, running postfix, spamassasin, amavis, sophos, sophie, clamav, freshclam, pop, imap, pop-before-smtp, gld, mysql, TLS, SASL...
You get the idea. It's a fairly complex setup. And it's all managed by smf. We're going to do a little writeup of this - stay tuned!
We did have one glitch. Looks like lockd (the nlockmgr service) doesn't always register properly with rpcbind. This caused command line mail clients like mail and mutt running on older machines to hang. (Solaris 10 clients were fine because they're using NFSv4 which handles the locking itself.) Having identified this, a quick
svcadm restart svc:/network/nfs/nlockmgr:default
brought everything back to life.