There's a lot of things that factor into SERP position. You may have 1000 IBL's, but a similar site with merely 100 IBL's that are more relvant and higher quality might rank better than your site. Simply having a link doesn't push you to the top of the SERP's, the quality of that link is a huge factor, more so than the quantity. By quality, I mean:
- Relevance of the linking sites content to yours
- title, header, and other important tag text on the linking site
- anchor text in you link on the linking site
- PR of the linking site(arguable)
- number of OBL's on the linking site(less is better)
- Your proximatey to the top of the page on the linking site
- etc...
I hope that helps.