I recently switched from blogger.com to wordpress.com (open source).
The major difference here being you install the software on your own site, rather than using blogger.com’s interface.
One problem I had (which I just now resolved thanks to the intelligent software support system on freenode #wordpress)…was that when I posted, the browser would hang for over a minute.
Actually, the problem is that I am “pinging” nearly 50-100 xml-rpc blog ping services, and that takes a time to ping each one serially. I suggested they fork the ping process off, or close stdout.
It’s not too big an issue for me, if your browser starts timing out, that would be annoying.
But the solution I would implement in the source code would be to fork the xml-rpc ping process and/or close stdout so the browser can return.
If you don’t want to wait for that to make it down to the release, you can also weed out a lot of the xml-rpc ping services because of overlap.