Well if you are a regular blogger, then Google Bot’s crawl rate on your blog will be pretty high. Which inturn means that your blog posts get indexed very soon.
Any new blog post in my blog, from my observation, usually gets indexed in less than 5 mins. However, since 20th October 2010, none of my blog posts were getting indexed. At first, I was a bit worried, only to realize that it was not some random problem with my blog alone, in fact a lot of other popular blogs are having similar problems.
I spoke to Amit Bhawani and he too confirmed about struggling with the same problem.
Read this post on his blog, which gives more insight into the problem: Google Indexing Problem