Hey guestcam,
I use wordpress for my blogs, but have recently looked into a few other solutions. Some are more suited for multiple authors, some run ASP.NET as opposed to PHP. Perhaps I can help you find what you are looking for. As Walrus said, bBlog uses smarty templates, so that may be useful for getting your designs going. From what I understand of it, you just take a tag which is formatted like {somefunction} and insert it where you want it to happen. I don't know where a list of all the tags are, maybe walrus knows. I didn't look too deep into the documentation. But, as was said in other replies, you will have pretty much the same default skins in each blogging package, very vanilla stuff.
Since there is such a huge ammount of porn blogs running wordpress, and I haven't seen any good skins for porn, I'm going to be making some skins soon. It seems almost every porn blog I see is running the same 5 skins. I'm making a bunch of skins for wordpress that are specifically targeted for porn blogs. I'd like to show you a sample, but I'm still working bugs out. I want to have them work right out of the box for people with no problems. Eventually I'd like to try to port these to other platforms, which is why I did the research in mentioned in the previous paragraph. It may still be a month before I roll out the first few, but if you'd like any advice on skinning a wordpress blog, or finding your way around the WP documentation, feel free to PM me.
Here is the link to bBlog, by the way:
http://www.bblog.com
And here's one similar to wordpress that looks pretty cool:
http://nucleuscms.org/ although they have very similar available skins.