Here are my final thoughts on themes, listed in no particular order of importance, just as they came to me as I was writing this.

• If you have a very clear vision of what you want and can't find a free theme to fit your criteria, consider either a paid theme or a theme builder.
• Unless you are getting 1k visitors per month and/or have AT LEAST 50 pieces of content, don't get bogged down with the appearance of your site.
  
• Premium themes are often well worth the price - they're better supported (you can determine this by looking at their support doco prior to purchase) and are more likely to be maintained/updated as Wordpress changes over the life of your business.
• Theme builders are an aweesome choice for someone with a background in graphic design. If you don't have that kind of background, you're going to waste a heck of a lot of time on tweaking the way your site looks and lose focus on making money.
• Even IF you are a graphic designer, unless it is a portfolio site to showcase your work, don't waste a lot of time on the appearance of the site. Again, content is king and it is what will drive customers to your site.

I hope this tutorial lived up to people's expectations. I'll be happy to answer any specific questions you may have now that it's complete (that is, except for 'what is a good theme for 'X'? - I just showed you how to choose).