I've registered totally new domain names for new sites I am starting and I've tried to make sure no search engines see them in their new stage when they don't have content.  The reason I don't want the search engine spiders to see them is that I want to have content up first so when they do visit they see something usefull up.  So I basically don't link to any new sites untill there is content up and the sites are structurally sound, meaning no broken links etc.  I've noticed though that new sites I've started are being cached before I even get a chance to put up content.  I thought maybe Google was somehow recording what new domains were registered but then I realized I use the Google Toolbar.  I often use the Google toolbar to jump to my sites.  I copy and paste the domain either in the Google toolbar or in the address bar of Firefox which is the predominent browser I use.  So because I visit my new sites when I'm working on them the Google toolbar is recording what site I'm visiting and quickly they send over their spider.  Now I don't see this as a good thing as I don't want Google spidering my new sites that don't have content, but this is a good thing when your site is built and you want Google to come check it out.