Yes, I may start hacking myself, but I'll list them here anyway:
1) Support for caching. I don't like that b2evolution sends headers to prevent caching. It would help with feed readers and browsers to not repeatedly fetch a new version and it would help conserve some server bandwidth.
2) Strict (X)HTML. I feel kinda dirty that my blog uses Transitional (which 12 years later, we shouldn't still be using).
General Support
b2evolution CMS Support Forums
1) I think this is addressed in the latest Beta version
2) It's not that hard to achieve Strict validation. I know Yabba is looking at the "search box" issue, but that's easily fixed yourself.