To nobody’s great surprise, the biggest player in search engines has entered the blog search arena. Folks, let’s have a big hand to welcome Google Blog Search.

Technorati‘s early lead in blog searching looks pretty vulnerable these days, thanks to some real (and acknowledged) problems with reliability and scaling. The exponential growth of the blogging world makes it very hard to keep up; so do the wiles of spammers and search engine fraudsters, who put up phony blogs to inflate their clients’ search results. That’s an area where Google has had plenty of experience, if mixed success.

Google’s blog search, which is still in beta, or testing, mode, has been indexing blogs since June. It boasts the spartan Google interface, RSS feeds for 10 or 100 search results, naughty content filtering, language filtering and the usual set of Google search operators.

There’s also a new set of search operators:

• inblogtitle:
• inposttitle:
• inpostauthor:
• blogurl:

Handy. But as far as I can tell, Google blog search doesn’t yet support tagging, which — given how central tags have become for blogs and related media — is a pretty big gap, and limits its usefulness for many custom aggregation functions.

So don’t count Technorati — one of the tagging leaders — out quite yet. Their server’s mighty snappy this morning, they found just as many of my posts as Google did a minute ago, and they have a warm place in the hearts of many bloggers, including this one’s.

Update: And Technorati is, officially at least, welcoming Google with open arms… and some free advice that looks more than a little like competitive positioning:

At Technorati, we have a tremendous amount of respect for the Google team and for everything they’ve done in the world of search. I’m sure that they’ll continue to improve over the coming months, perhaps including tags, recent images and links, zeitgeists, blogger tools, and other types of semistructured data. I’m sure that they’ll also start indexing the full-text of blog posts, not just the partial text found in most blog feeds.

I welcome the competition. We’ve got some tricks up our sleeves too – and there’s no doubt that in the end, the competition will end up producing more innovation and better services for bloggers and readers.

Meanwhile, here’s a classy little touch: Technorati’s community manager, Niall Kennedy, tipped the folks at Ping-o-Matic to a Google-centric news story that plugs the Ping-o-Matic service.