Theres no worry of duplicate content or anything like that is there? i guess there shouldn't be, but what do you think? is it quite ok to add a blog post to more than one category when it makes sense to? Sometimes some posts seem like its sensible to add it to 2 categories because the post content and both blog categories are fitting.
I don't see an issue with it. Most search engines should be able to tell the difference between and individual post page and category page. You could make certain changes to your template and wordpress settings so that the category pages had robot exclusions or something to prevent them from being indexed and ranked separately from the post pages, but I think that it shouldn't be cause for duplicate content.
The all in one SEO plugin has an option where you can make the category pages non indexable.. Some people would say that it is OK to add more categories, and google knows a blog category from a genuine duplicate content, but you never know, and it is always better be safe than sorry. Like I said, use the category as feature to give easy access to visitors to same category posts, but it is best kept unindexable. And when you are going to add a post to multiple categories, all the more reason to make them unindexable.. I go with the assumtion that, it hurts none but it has no SEO benefits either. And you never know when google starts treating them as duplicate, since they are duplicate in the first place. I am saying this because more and more SEO type guys are using wordpress to create Websites for SEs, and I think there are more WP as a CMS sites than genuine blogs.. I have had instances where one of my category pages ranks for well for a few terms.. On those Sites I have left the categories Indexable.. And have modified the category pages so that there are enough data below each posts on the category pages to make them look unique.. But on new sites, I make it an effort to make them non-indexable. All in One SEO plugin has the option.