Important thing for the logo is that the q should almost read like a cj it should not confuse too much that people are typing the wrong thing, but it would be good if it was recognizable. The Q is more important then the cj as the Q is in the url. From what I have seen so far I think the name is best in uppercase, but feel free to dissagree.
The logo should be usable on its own and small. Please note that this logo is the only branding most people will ever see! So actually adding the .com is preffered but it doesn't have to be on the same line perse.
I guess I like the simplistic logo of DISQUS (also note that with the comments form there is a color difference (f.ex. Inc job as two diferent shades but on the main page this is not used.