FearOfCamelNotation (Using capital & small letters in web & email addresses)
Which web address is easiest to read?
Obviously, www.ThisWebAddressIsLong.com is the easiest. The capital letters tip you off as to the beginning of each word embedded within the address.
Using capital letters within text like this is called "camel notation," because the capital letters in the middle of the text are reminiscent of the humps on a camel. It's a common practice in the computer world used to make multiple words strung together more readable.
Less memorable advertising
As a techie, I've often wondered why camel notation is rarely used in advertising copy. More often than not, the web address listed in yellow pages, newspaper ads, and business cards uses all lower (or sometimes upper) case letters, even when it makes the address difficult to read. This means, of course, that it's also less memorable, which is not what you want to accomplish in your advertising.
I imagine that the primary reason camel notation isn't used more often is that there's a lot of confusion over what is, and what is not, case sensitive. The fear is that if the wrong case is used, the web address won't work and the dreaded "HTTP 404 - File not found" error will appear. And that's not a good thing to discover after your business cards have been printed!
Left side is always safe
So, when is it safe to just arbitrarily use upper or lower case letters without any worries that the address won't work? That answer is slightly technical, which I'll explain shortly, but if nothing else, remember this rule of thumb: everything up to, and including, the ".com" (or ".org" or ".net", etc.) portion of the web address is never case sensitive. This means that you never have to worry about whether www.example.com, WWW.EXAMPLE.COM or www.Example.com will work. They all work just fine, so use the one that looks the best to you.
Domain Name Servers – directory assistance of the Internet
The ".com", ".org", ".net", etc. portion of a web address is called, in Internet parlance, the "Top Level Domain," or "TLD" for short.
So, why is the web address up to, and including, the TLD unaffected by case? It's because it's used by special computers on the Internet called "Domain Name Servers" to locate the exact web server associated with that address. Think of Domain Name Servers as the phone directory of the Internet – they match the "friendly" web address you type with the exact computer (among millions) that "houses" the website you want to see.
And this system doesn't care one whit whether you use upper or lower case letters – it treats them all the same.
"Bad" file names! Bad!
However, the part of the web address that comes after the TLD is not used by the Domain Name Servers. This part is literally a file on the web server that was located by the Domain Name Servers. For instance, for the web address of www.example.com/FAQ.htm, the "FAQ.htm" portion is the name of a file on that web server's hard disk.
This is where the case sometimes makes a difference, depending on the operating system used by that web server. Windows servers do not differentiate between upper and lower case letters, but Unix/Linux servers do.
Think for a moment about the files on your computer's hard disk. If you're running Windows, you might save your work using a file name of "RESUME.DOC". With Windows it doesn't matter if you later try to open up that file by using the name of "resume.doc". It will open the same file.
However, if somebody on a Unix (or Linux) computer saves a file called "RESUME.DOC", then later tries to open it using the name of "resume.doc", Unix will complain that "resume.doc" can't be found. That's because to Unix, they're two completely different files.
Similarly, when a web server is running on Unix, "FAQ.htm" and "faq.htm" are considered to be completely different files.
What about e-mail addresses?
Website addresses aren't the only things that suffer from "case paranoia." I've also noticed how often non-techie folks explicitly state whether their e-mail addresses are upper or lower case. With e-mail addresses, practically speaking, the case never matters.
(According to the official Internet specification, there is a part of the e-mail address that's supposed to be case sensitive, but in real life, e-mail systems almost never differentiate between upper and lower case. I've never personally encountered any problems that were caused by using the wrong case in an e-mail address, and my research hasn't uncovered anybody else who's had problems with it either.)
The bottom line
So remember, with web addresses, everything up to, and including, the TLD (the ".com" part) is never case sensitive (e.g. www.example.com). But any text extending past the TLD might be case sensitive (e.g. www.example.com/FAQ.htm). And e-mail addresses are never case sensitive.
This means that you can use both upper and lower case letters up through the TLD portion of a web address with reckless abandon.