Personally, I do believe in a sandbox, but I do not believe it is applied to all websites, and you can kill the sandbox effect via strong links.
My April 6 site has two incoming links; one from a PR5 page of mine, another from a PR4 page purchased here. If the sandbox exists, how have the last two sites I created bypassed it??? (different niches - one holiday related, the second pet related)
I only heard of the sandbox recently and I see how it works. I have two sites, same niche, one is nearly a year old, one is coming up on 6 months, or so. The older site is doing great in Google, 2500+ visits from Google weekly, the other site however is only getting 200 weekly, not ranking for any competitive phrases.
On my first site, the day it was 'released from the sandbox', i went from 300 hits a day from google, to 3500-4500 on average. It took me about a year on this site, although the first 5 months I really did 0 optimizing I had no idea what I was doing, I was making this site for my dad. (fashion, handbags niche - so semi-competitive)
Some of my sites get boxed pretty hard and some dont get boxed at all. I think it has to do with the size of the website and the number of outgoing links and reciprocals and possibly, if the domain has been expired before and then subsequently reregistered.
Pages, not sites. If you start a blog (and setup some links from your older domains), in 1 month you will have some pages in the main index. The other will remain sanboxed (as you call it).
i dont know the name of this filter for new sites (sandbox or trust rank) but i know only one think G applies a filter to new sites
I have never seen any evidence that a sandbox exists. I have had sites for many years, some get indexed straight away, some take a bit of time, but nothing that points to a deliberate thing like a sandbox, it's pretty much random. I have quite a few domains that I use pruely for redirects but I usually place a sentence on them just to see what happens. A lot of those domains are indexed the day I put them up with visits from Google and a couple have actually reached the first page of Google for the term I have on the page. They have no backlinks of any sort. it's a total mystery to me ... but then it's not a mystery at all .... Google is such a beast anything can happen for no reason, good or bad, it's like a lottery.
the sandbox surely exists its a effect of the size and volume of google, they keep you there for a certain time to see if your relevant. Once you start getting links etc to your top keywords ive found you generally start to show signs of moving out of the box.