Google did this with one of my websites too. The site had inbound links from many PR3-PR5 websites, stats showed googlebot making visits to the website. However the site was not getting indexed in google. It didnt appear even for "domain.com" or "site:domain.com" search. It remained like this for 8 months. With recent
PR updates, it jumped to PR4 and now has more than 500 pages cached

.