Right so why have a tag cloud? What would be their purpose? Do they have any purpose regarding spiders?
I dont think they have purpose regarding spiders? Theya only are to attract attention of your visitors.
I've noticed them used on niche(non-mmo) sites and homepage/personal sites.. That's about the only place I can see them be really useful. In most circumstances I would say it's not too useful to have.
They make it easier for your readers to navigate. If you made a post where Dimitar Berbatov was the key element, and categorised it under Manchester United, and then wrote a random post on Berbatov's personal life ( in the general category), the Berbatov tag can help users navigate to those posts about Berbatov which would be useful to them. The search button would throw up every post where Berbatov is present ( even ones where he is not really the focus of the article), and it becomes difficult for the reader to get what he wants.
works well for certain sites of mine (like vidology linked in my sig), not worth it for others which have a ton of unique posts/tags. i dont even use tags on my tech site, just categories.
If you are using WordPress many use a plugin called 'all-in-one-seo-pack' to improve SEO. Most who use this plugin have Google bot NOT scan the Tag cloud to eliminate possible duplicate content problems
Hey due to such tags, your blog have many pages crawled with same contents check how Google have indexed your blog pages by searching site:vidology.com. I highly recommend do not use cloud tags or categories.