No they don't. They just pick up your text, unless you actually have a page that has the tags as text. For example, if you were to write a tutorial on how to create a website and used <table> tags to explain it, they would show up. The actual coding however would not.

As far as using tables excessively, be only a little cautious.

Excessive use might hurt in a "quality of code" evaluation... which although really unknown, might be one of the hundreds of points used to grade a site.

Excessive nested tables is what I'd watch out for.

Tables can also be a very powerful SEO tool, nested ones to, in well SEO'd sites.

Because search engine spiders read a page like the 'Lynx' browser, they are reading content as it appears in coding.  A popular SEO technique is to create a table with blank <td>s to elevate keyword rich content (this way it is indexed first.  wouldn't the subject matter of a page be first, right?)

Another SEO concept to keep in mind is coding to content density.  Overall, if you have an intensely coded html page... you might want to rework it.  This is thought to be one of the reason that many of the WIZIWIGs don't index too well.

One of the last thoughts is that again the most important content should be first, early on and quickly read.  Embedding stylesheets will raise your content to code ratios.

It is thought that spiders really read only so much of every page.  If you have many tables, you might just have too much content on the page.  You may want to consider making additional pages for the content.

IN the end, you'll have to decide how much time you will want to spend on a SEO effort.  It does payoff, but, you can really go nutty and find yourself designing for a search engine rather than for people.

Good luck,
Starke

As far as I know, the only way to raise your PR is to increase the inbound links to your site. The more sites that link to you (with relevant content, to boot) the higher your PR.

Anytime you redesign a site, you risk losing ranking for a short time. I had one of my sites redesigned. I was ranking #1 for my keyword. After the redesign, and a poor one in SEO terms, I dropped off the organic listings, but only for a short time-maybe two weeks. I checked now, and I'm number three.