as dynamic of link building matters I will describe situation with a timeline:
1 stage (1.5-1 years ago). I have done good work of optimization and link building etc. Was get good rankings in Yahoo and MSN, but no at Google. "Sandbox and Google requires patience", I've thought and forgot about site, just doing some links time from time
2 stage (1 year - 2 months ago). Time from time I've build a few links and added several pages. Site has been seen in TOP10-TOP50 for several relevant key phrases (TOP10 - less competitive, TOP50 - most competitive). Best results where in January 2006 in Google. In that time site has fallen in MSN/Yahoo, thats because I was not working constantly on it, its okay.
3 stage (3-2 months ago). Redesign of the site (content still the same) and I start a heavy link building campaign. Site's positions in Yahoo/MSN grew up and are good now. But site have disappeared (after Google indexed new version of site) in Google completely, and even when I ask for domain name (without .com) I only find it on 15th place!
Is it due to site redesign and high number of new fresh links? And all is needed jsut to wait a few months...