Basically the google site search only searches the blog front page, so searching for something like "travel blogs" on my site would return no results, even though there is a post by that name in the archives. However using the google blog search returns the results as expected.
I can only assume that google is doing this because their main index is getting just too damn large with all the blogosphere activity, and specialised search is the way to go.
I wonder though, what this means for searching in the long term. The idea that people have to now do a normal google search and then maybe blog searches to find what they're looking for might bring back some popularity to meta-search sites again.