A Google Webmaster Help thread has advice from Googler, JohnMu, on how to help get your blog included in the Google Blog Search index. John said to basically manually ping Google with their pinging service.
To do so, go to http://blogsearch.google.com/ping and add your blog.
We use blog-search pings to pick up blogs. From what I heard back, at the time of the last ping there were some small technical issues with your site, making us abort the fetching for Blog-Search. A simple solution to that is to just do a manual ping via the web-interface ( http://blogsearch.google.com/ping ), which is what I did yesterday. Apparently it's been picked up now and should be trickling through the pipeline soon'ish :-). This is usually not a problem, especially when the blog regularly adds content, then missing a single ping won't break things. But if we really rarely see blog-search pings, then missing any of them can cause hiccups like this.
So my recommendation to sites in a similar situation is to do a manual "ping" (and double-check to make sure that you're really pinging Google's Blog-Search automatically), and generally to work on regularly adding content to your blog. That said, keep in mind that your content will be available through our web-search regardless of whether or not it's seen as a blog or also indexed in Blog Search :)
To be honest, it seems to me that Blog Search is slowly being phased out in exchange for a focus on real time search. The last time we really wrote about Google Blog Search was just about a year ago. So I am just under the impression that Google is not caring much about blog search and focusing efforts in other areas - which is fine.
Do you think this is true and if so, is it a bad idea?
Forum discussion at Google Webmaster Help.