I have seen some complaints about Google indexing before, so decided to answer as I do not have any such kind of problems. After I publish new blog entry it will be shown up after 2-3 days so maybe the problem is somewhere else.
1. Did you refresh the content or is the content same? How frequently you are refreshing your content?
2. Do you have same incoming links? Maybe publishing it with tags to content aggregators will help? Also allow user to bookmark your site with del.icio, technorati, etc. All those links are considered as incoming links for search engines.
3. What kind of key phrases you expect your site to come up? Maybe changing those will help. One of google algorithms is to follow users behaviour. So, if you didn't get much clicks Google thinks, it's not relevant content for particular search.
4. I took a look to your sitemap. There is no XML code at all for sitemap? The proper format is:
<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex lns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap>
<loc>http://www.example.com/sitemap1.xml.gz</loc>
<lastmod>2004-10-01T18:23:17+00:00</lastmod> </sitemap> <sitemap>
<loc>http://www.example.com/sitemap2.xml.gz</loc>
<lastmod>2005-01-01</lastmod>
</sitemap>
</sitemapindex>

Hopefuly it helps. Veiko