This is my scenario:

2 basically brand new MT installations on different sites and different servers, one is 4.01 the other 4.1. When posting to the 4.01 blog Google picks up the posts within minutes, I can almost immediately see them in their index.
Today I started posting on the 4.1 blog. No error message when pinging but even after hours not a single post appears in Google.
How can this be? I thought about the server with the 4.1 installation blocking pings but pings to Technorati went through. Any ideas? I'm pretty much a newbie to MT.

Just tried again, with the same result. Pings to Google result in articles on the 4.01 installation getting listed within minutes, on the 4.1 installation still not a single one after one day.

I doubt it's an issue with MT, but probably a delay in your site being crawled on Google's end -- which could be for a variety of reasons. Over the last 10 years I've learned to never expect consistency when it comes to search engines, particularly Google.

Thanks, Justin. You're probably right... The funny thing (not!) is that the site whose posts don't get listed is the one which is much bigger, has a lot more pages listed in Google and is a lot more active overall. But well, I guess I better don't try to understannd Google...