A few Thoughts:
1: From what you've said it sounds like you're editing Thematic directly. I would advise strongly against this, you should use a child theme, it has SO many benefits, too many to list here but in a nutshell, if you develop your website in a child theme it will be protected from future upgrades (thematic is updated on a regular basis) and retain all that unique styling (such as your desired lowercase styling). If you continue to edit Thematic directly you will lose updates when Thematic itself is updated. Also you may break something in Thematic, editing the PHP files directly is not recommended. The good news is that building a child theme is easy once you know how! For more information and before you do ANYTHING else I would highly recommend reading this, it's short and tells you why: http://themeshaper.com/2009/04/17/wordpress-child-theme-basics/
There's more on child themes here: http://themeshaper.com/thematic/guide/?page_id=66
If you look in Thematic file you downloaded it comes with an example child theme, look inside your Thematic download file for the folder "thematicsamplechildtheme". When you alter a style in your child theme it overrides the parent theme (Thematic) styling so you can have your website as you want and upgrades don't lose all your hard work styling it to get it how you want!
2: What you're looking at changing sounds like a CSS issue. So, for example, you identified that "#comments-list .comment-meta" needed changing to make the text lowercase and you edited the CSS. The second big tip of the day which will make your life SO much easier. Get firebug for Firefox. Once you get this you can use the tools in that program that help you identify what DIV or CLASS you need to change to get your desired styling in your child theme stylesheet.
If you post a link to your website we can look at it, but you will be so happy once you see what Firebug can tell you and it will enable you to get your website how you want it. Remember, I would recommend using a child theme before you do anything else, you'll almost certainly be happier and understand why when you read the article above I suggested and implement it.
Someone else here might have some other thoughts but that's my advice!