I have heard browsers do not like you using capital letters in your address. Is it really going to effect my SERPS? I heard the browsers revert to lower case and so they may get a 404 page instead of your actual page. Can anyone answer this for me?

Thanks!

Since only directory and document names can contain capital letters, you're limited to using them for those purposes. While you can display your domain name on your webpages with capitalization or even use capitals in links to add a bit of style, they will all be normalized to lower case as browsers and search engine robots encounter them.

If you use mixed case for document or directory names, you need to be sure to be consistent in your spelling when you create links to them because the search engines will see different spellings as distinct URLs - which is as they should. Browsers don't have a problem with mixed case use because they simply use the URL as-is (whether from a link, a bookmark, or typed directly into the address bar) and rely on the site's server to handle the request.

Where mixed case can affect your rankings is on Microsoft IIs servers, because they are case-insensitive. That means it will serve the matching document, even if the URL is "misspelled" in terms of capitalization. So, if the search engines see the same content served from multiple URLs, you can run into duplicate content issues. Apache is case sensitive, so when it receives a request that is "misspelled", it returns a 404 error.

In any case, the best practice is consistency. If you use mixed case in your document and directory names, be sure to use the same spelling in all of your links. For simplicity, many people recommend simply using lower case all the time, but it's up to you.

Thanks, so it really makes no difference whether my Url's have capitalization where it makes sense to capitalize a word?

Thanks, so it really makes no difference whether my Url's have capitalization where it makes sense to capitalize a word?
Not sure that is exactly what rainborick is saying, depends on what you mean by "URL".

Case variations in directory and filenames result in separate URLs. As a result Google may crawl all 3 treating content at each as a unique page. Because each contains the same content, duplicate content issues can come into play.

IE
/Page.html
/PAGE.HTML
/page.html

I'm pretty sure, IIS servers are always case sensitive when it comes to parameters in URLs.

Case is also important depending on your site's use of: site search, analytics, URL patterns, URLs in search results and/or Robots.txt directives for private data as well as other since all of these may be case sensitive.

This question comes up lots because when a user types a query in Google's search box that user query is treated as case insensitive. For example, [ new york times ] & [ New York Times ]. These issues are two different issues but often assumed (incorrectly) to be the same.

Yes capitalization in URLs matters but "Officially" capitalization in Google's search box doesn't....

Hope that helps and best of luck!;)

Windows servers do not differentiate between lower and uppercase letters but Unix and Linux servers do differentiate. When somebody tends to click (through browser) a page with lowers case letters from organic results or referrals but actually the page would be created with uppercase letters then this leads to a broken page. It is advisable to have lowers case letters that can support all situations in all trends :)

Best,