I have had issues with Wordpress upgrades in the past. Nothing makes my day like going through the upgrade process, refreshing the page and getting a nice clean white screen. And then activating the plugins one at a time to find the culprit.
But with 2.5, I've had no issues yet. Of course, I've not upgraded on my two my main blogs yet. But the upgrade went through without a hitch on three other sites. I use the same set of plugins and only activate as needed on new sites. My plugin folder is about 12 MB in size. If something was going to screw up, I think it would have.
As far as using the interface goes, there is not much difference really that I can see. Different colors, different icons, things in different places. But for the most part, I knew where to find everything.
Getting back to plugins, there is one function I like in the new Wordpress. You can update plugins by clicking on a link. But like I said, I have a lot of plugins. So I found one that will update all of your out of date plugins with one click.
I have been staring at the plugins that are out of date at my blog for a while. Some day. There's a lot of them. Plugin central took care of this with only about 2 seconds of my time.
One of the issues I had with expanding the amount of blogs I have was that I knew I could never keep everything up to date. If ten plugins needed updating, they would need updating across all of my blogs. This could take some time.
Now, though I can go ahead with my plan of having one pristine, perfect installation of Wordpress that I will use to build all the new blogs. And while originally I was going to have one pristine folder of plugins that I would use to overwrite the old folder on updates, I can now just login and click a button.
Now I just have to install 2.5 here. I have heard issues with the Automatic Upgrade plugin and 2.5. With the other blogs, I used Dreamhost's oneclick to upgrade. With the two on my server, I didn't have the foresight to use Fantastico to install Wordpress. So we shall see.