Hi
As a second point, the Yhc team do a variety of builds - some from clean, some from fullclean, some from delete the directory and a completely fresh darcs pull etc. We've found that can help catch things like interface changes, dependancies etc earlier. If you have (or can find) too many Windows/Linux machines etc that might be worth doing - and is pretty easy with buildbot.
As a side point, if you are considering becoming a GHC buildbot slave, and are going to go to the (admitedly pretty small) trouble of installing buildbot etc, you might want to consider becoming a Yhc buildbot. Being a Yhc buildbot takes very little processor power and time - builds take between 3 and 15 mins. Our existing list of buildbots is http://www.indiegigs.co.uk:8010/ , and our details on being a buildbot are http://haskell.org/haskellwiki/Yhc/Buildbot . If you do want to be a Yhc buildbot please drop yhc@haskell.org a quick email (cc'ing me, since we've been having some issues of posts bouncing from non-members) Thanks (and appologies for being so off-topic on GHC-users!) Neil