I just wonder how search engines looking at tag cloud features, most used on wordpress of course. Can it lead your site to be penalized? Even not use them as spam I think it may lead your site being penalized one way or another. What do you think?
If one tag is used for only one article, this is a problem. Article A have tag AB an AC. so when you go to AB the article is only A, and in AC there is only one A article. This makes them both nearly have similar content. What I do is make the tag page unique by displaying content from amazon using my own plugin.
Normally NO, tag clouds lead to inner pages so there's no question of you getting penalized. The best way to be safe is by adding the 'nofollow' attribute to your tags. You may want to check this post about adding 'nofollow' to links within the tag cloud.
If you have only 2 blog posts in your blog, don't activate tag cloud yet. Wait until you make abou 20-30 and there you go.
I am against the suggestion that a tag cloud is necessarily positive or negative one way or another - it depends on the way tags are constructed, and number of tags there are in the cloud. If you are fairly preventive about what's including in the tag cloud(e.g. by having set tags as opposed to allowing a free entry) then you're very unlikely to run into problems as I think. Of course, one shortcoming of tag cloud is that virtual importance is displayed visually (i.e. with a larger font size for most recurrent tags) which isn't communicate to search engines. Of course, keywords used most regularly in tags will also be linked to most regularly from articles, so tags themselves need not bare from this problem.