When (or if) can I expect the sandbox effect.

[fatpeter]

O.K. So I have tried to be a little clever and I'm not sure if I am gonna get away with it or not!

I bought a domain I liked about 3 years ago and put up a small website on it... lets say about an individual widget.
I gained a few links to it (mainly from sites I own but a few independant ones) and left it to cruise along on it's own for 3 years.
Middle of November the site had about 30 pages and a modest 15 backlinks.

I have redirected those 30 pages with a 301 redirect to their new place on the web and that new site is indexed and ranking o.k.

I have launched a new all encompassing website about widgets using this domain which started off with 240 pages of content which has increased steadily to 700 pages with user inputed content over the last 6 weeks.
The site has gathered about 300 inbound links over this period. Yahoo is showing 800 but I think that is a bit optimistic!

I fully expected to be sandboxed as I thought the increase in inbound links would be pushing my luck but so far (fingers crossed)
the site is ranking far better than I expected.

All 700 pages are indexed in google..about 100 are supplemental which I expected as they don't have much content.
All the other pages are ranking along with the other well established sites in this sector.
Site is static html with all dynamic content blocked by robots.txt
New pages added daily are finding their way into the index in under a week.

I know all the talk regarding sandbox not existing but I am also aware of new sites ranking well initially and then disappearing.
I am wondering if this is going to happen to this site.

One other factor which is probably unnatural. The site has no outbound links. All links go through the cgi-bin and a script.
There is no advertising on the site at the moment. Well, no adsense but I have people paying me to appear on the site.

This has been a long term plan. 3 years ago I started a similiar site which took a long time to rank well.
Now it does o.k but this new site is ranking better than my old established site for many queries which has me a bit puzzled.

I am watching my visitor numbers climbing steadily and am wondering when it will all come crashing down?

Is it possible that the age of the domain and the fact that the topic hasn't changed is going to save me the pain?

Anyone with similiar experiences?