There are certainly no "rules" for this kind of naming and/or branding of things.

Using hyphens in such cases (as in, Para-sail, Post-it, Q-tips, Snap-on — all trademarked brand names) is another option, but one that is somewhat out of fashion these days.

Personally, I think that using internal capitals (as with, PowerBuilder, WordPress, and PowerPoint) should be avoided where there is little or nothing to gain in clarifying the pronunciation or the meaning, or emphasizing a distinction. Why not just Powerbuilder, Wordpress, and Powerpoint?

YouTube, I think works well because with "Youtube" it is not exactly clear that this word is not actually foreign word — perhaps pronounced 'yout-ubé ?

For WikiSpeedia, I think a similar case can be made. It is one word like "Wikipedia" but it is different, and that difference is emphasized by capitalizing the "Speedia" part. In terms of branding at at-a-glance recognition, it does seem that there is much to be gained.

If we were in the 1970s or an earlier time, "Wiki-speedia" would probably be the clear front-running candidate. But, these days, FedEx and YouTube will win out every time over Fed-ex and You-tube.

When to close the compound (Stackexchange) and when to leave it open (Stack Exchange) is also mostly a rhetorical issue. Why not Word Press, for example? When the words are common, closing them makes it clearer that what we are talking about is a single brand name a single "mark." But when the compound created is awkward or risks looking unpronounceable, then you either have to open them back up, hyphenate them, or use internal capitalization. And that takes us back to the start.