On the WordPress.com home page there is no Search box to input a category/tag that does not appear in the tag cloud. This makes it quite difficult and/or cumbersome to find posts.
For instance, I am a photoblog showing images only (apart from the post title). I think it would be ridiculous for me to have on my blog a category called photoblog, just so that others in the WordPress family/visitors to the home page can find any of my posts. As well, because I *am* a photoblog, the categories I create relate to the subject matter and are not always obvious categories, eg flowers, It seems the only way for me to find any of my flowers posts, in that home page tag cloud, is for me to click onto Nature and then hope for the best that there is a further sub-category, in the right-hand sidebar, that says flowers (which there is of course; this is just an example).
For instance, I also have a category called Plants, and this covers plants other than flowers. Normally, I would categorise an image of, say, nothing but a lovely tree, as Trees, NOT Nature, Plants, Trees. For me, one tag says it all! Why should I have to have three categories to say what one tag can say?!
The WordPress database software *should* be able to generate tag clouds covering the not-so-obvious categories, as explained above. Otherwise, have a Search box; that makes better sense to me! Ditto re finding blogs by name, as is usual on other online directories.