Doubts about tags

I have several doubts about tags.

Before upgrading to version 2.3 tags were not implemented and I used to use simple tagging plugin to tag all the posts, get a tag cloud and, most important to me, display a list of related posts.

Now, with version 2.3.x, tags are implemented and the use of such a plugin may be unnecessary. Is that true? Is there any problem to use both options? (let’s say as a way of displaying in WP’s tags a localization and un simple tags’ plugin displaying “key words”)
How can I display a list of related posts with default WP installation?

Thank you