I've been doing some research lately with MOSS for Search installations. I came across some interesting blogs when it comes to search. One of them is Mike Taghizadeh's Blog, a useful resource.
Dan Attis mentions his latest post about MOSS Search boundaries. It seems like the SharePoint boundaries for search, but also in general have a lot of potention to grow big.
Of course, you already knew this. ;) But it is alway good to see the actual numbers. When you're busy planning your SharePoint deployment, these boundaries are very usefull.