Well, it is unclear whether you’re asking about how many levels deep it is in terms of directories or how far it is from the root page. One way you can make sure that Google reaches those pages is link from your root page, your main page, directly to the deep pages that you want to get crawled. So, we tend not to think about how many directories deep a page is but do look at how much PageRank a page has.
So, if a lot of people link to your root page then you can link to subpages and then those subpages can link to other subpages and at some point, then we’ll stop crawling. So, one thing you can do is you can try to make sure that as many pages as possible are within just a few clicks from your root page.
Either pages convert the way that you want or they have really good ROI so, don’t treat all of your pages the same if you got a few that are real just like moneymakers, try to surface those and get them kind of linked to from your root page so that you can make the most out of that.
by Matt Cutts - Google's Head of Search Quality Team