Theme code not fit for WordPress 2.3.3 can be dangerous. I found this out the hard way.
Yes, it matters. You cannot simply upgrade the core files,you must also make sure tags and hooks in your theme are compatible as well. I’m afraid you are sort of on your own there,though.The WordPress Codex is not the most up to date batch of articles and it is from there that I have been gathering my little bits of theme info.
Which makes me wish there was a comprehensive list of tags and hooks and etc that have been definitively depreciated so that I can be sure not to use them ever again.Well of course they tell you what’s been out since 1.5 and 2.1 but not much else…
The best I could tell you is to grab a copy of an approved for 2.3.3 theme and explore its guts, comparing the code you tend to reuse with their’s and try to get up to date.
Or just keep triggering errors and wondering why, God, WHY?
I was able to find an answer in the WordPress forums despite the fact that it seem as though 98% of the questions go unresolved. But this is only because no one ever bothers to search the forum threads so the same questions get asked over and over and it tires the experts out to keep answering it.
I’m not absolutely sure that this is right but I’m pretty sure the theme code in the 2 default themes that come with every WordPress download are up to date. I hope so because I usually rely on Default for help.