I'm still using XWiki 4.3 milestone 1 on my personal web server.
It is not very useable as a blog since
1) very wide images aren't resized to fit the width of the blog
Couldn't you limit the size of the images either through wiki syntax ( [[image:foo.png||width="200px"]] ) or through CSS ( max-width: 200px )?
The size should be adjusted automatically without any funny CSS or width configuration. Otherwise, I'd end up coding a blog on top of XWiki.
2) There don't seem to be pingback or other XXXbacks used to communicate with other blog articles.
I don't know anything about this, so nothing changes on this part I guess.
3) For non-web devs or non-technical people, it is not easy to change themes or customize UI to make it look like a blog.
Nothing changed here. You can use either the Color Themes (for non-technical people) or you can customize the skin of the Blog space but you need to know a bit of CSS (and maybe some HTML/Velocity).
Probably.
The latest stable release is 5.1 now. Has it become useable for me?
If you're using XWiki only for the blog application then I think there are better alternatives (blog platforms) that were made specifically for this. XWiki's main goal is IMO to help you and your peers organize your information in a collaborative way. The new things that 5.1 brings compared to 4.3M1 are: new search engine based on Solr, virtual mode is on by default, new security module, new localization module, improved Distribution Wizard and Extension Manager in general.
Hope this helps, Marius
I guess wordpress is a perfect fit for a blog starter. I'm sad that I need XWiki for a wiki and wordpress for a blog.