From the amount of questions in the various threads it looks like we need some place to park all the various tidbits for buying Username options.
General notes:
This website posted by Sundance can allow you to play with colors and some (but not all, specifically shadow) of the effects. This will help you to find what colors you like together. If you do NOT want to see Italic and Bold, leave the fields empty, otherwise it will apply them anyways.
The background color behind your username is #666666, so when picking a color you should probably try putting that color against yours and see if they still look good together. You can use just about any program, including the site above, to compare colors.
Username colors:
When picking a color you can either use the color's name or the hex value of the color that you want, if there is no name for it (or you don't feel like trying to match a color you know to its name). You can get the name of a color just by selecting a color in a post then seeing what "name" the color was given, like this:[color="YellowGreen"][/color] would be
YellowGreen. You can also use "Chart 2" on the test site listed above to see 16 base colors that you can use the names for.
When you use a hex color, you MUST put a # on the front of the number, like this "#A0C0C0" otherwise the color will not be visible to most people (it will appear white instead).
When a Paid Subscriber buys a username color, this color will not take effect if they buy no other username option. The board's default color for the paid members is applied to the username after the color purchased in the Store. This will not occur if you buy something else for your username like Bold or Italic and you will see the color you buy. In the alternative, you can contact a benevolent moderator to assist you in making the color purchase take effect without having to buy anything additional.
The Bold applied to a Paid Subscriber's username disappears if they buy a color for their name. Thus if you do this you will need to buy back the Bold that was applied to your username.
Bold, Underlined, and Italic usernames:
These are pretty straightforward. These can be used to make your custom color appear if it won't for some reason, though this does not always work. I don't know what effect the underline has on the username with the usernames being underlined by default anyways, but it may cause the underline to become colored as your username in non-IE browsers (but don't hold me to that as I'm not sure!) Remember also that Paid Subscribers are by default Bold type but that is lost when you buy something like a color.
Username Glow: example: 
This adds a colored glow around your entire username (but not the default underline). All of the color notes that are in the Username Color section above apply to this as well. Note that people using any browser other than IE will not see this feature, as the glow function is a proprietary IE function.
Username Shadow Color: example: 
This adds a 3D shadow to your username the shine down and left from your name. This uses the same color rules as Glow and username Color as above. This function is also only supported in IE, just like the Glow function, so other browsers may not see the effect.
This function is not testable on the test site above; using that site with a color set for the glow will give a ROUGH approximation, but keep in mind that isn't what the final product will look like.
Username Font:
This changes the default font for your username from the board's default of Verdana to something else. Keep in mind that if you use some strange font that you "found on the internet someplace", other people are not likely to see that font. It would be best to stick with general fonts like Courier, Times New Roman, Arial, etc. so that what you choose, everyone can see. Wingdings is not recommended but might provide some humor if it works.
For Windows Users:
Selection of fonts for Windows users should be based on how the font *type* is shown in Character Map. (Character Map can be accessed through the Start Menu, under Accessories, in the System Tools folder). Fonts which display with a Black-and-Blue O appear to work fine; those with the TrueType font logo (Doubled Ts) may or may not work, based on my experimentation. In general, TT Fonts that were a single word in name functioned; those with spaces in their name tended not to function. YMMV.
Change Username:
Yep, does what it sounds like it does. No clue what trying to set your name to another user's name might do, I would think that aside from making people angry it may be a BAD thing to try.
If anyone thinks of other stuff post it and I'll update this post with it.