I think it needs to be said that, except in certain special cases, neither meta keywords or tag pages are likely to help you rank in Google or in the other major search engines, and excessive use of tag pages is commonly assumed to contribute to Panda problems in Google.
The keywords first...
Basically, meta keywords have been so misused that the engines disregard them, preferring to go with more visible signals. I thought they were considered dead and buried years ago, but discussion about them periodically resurfaces. Here's a link to what I believe is our most recent such discussion in the Google SEO forum...
In response to the premise of the thread, I posted the following...
meta keywords still do matter
Only in an oddball case like this one where there are presumably legitimate links pointing at the page, but the text isn't reflected elsewhere on the site. The situation illustrates how Google's anti-Google Bomb filter works, and it tells us that an occurrence of the term in the meta keywords will disable the filter.
If your site is all Flash or all graphics, with no text content, having the keywords in your meta keyword tag will provide a "confirmation" for Google that it's OK for inbound links to help the site rank.
As for tag pages, they can be set up in various ways... as several webmaster-defined "tag" links at the bottom of an article, eg, taking you to tag pages which link to related articles... or they can be user-generated tag pages, doing much the same thing.
Their drawback is that they tend to be seen as internally duplicated "shallow" content by Google, particularly if they only link to one or two articles each... and that's a drawback for users too. Lots of these, as can sometimes happen if they're in user-generated tag clouds with no tight limitation on the number of tag links, will add a lot of mostly empty pages to your site. Also, a large number of tag links can dissipate the link juice perhaps better used in a prioritized hierarchical navigation system. This can put your site on down side of Panda.
Much better, IMO, would be simply to expend some effort maintaining related links on the site, and to link to related articles directly from the article pages, with no intermediate tag pages.