First, I want to start off by saying that Xomba is a really great site. It doesn't have the more sleek look of a Hubpages but it is a cool site to read great articles and bookmarks. It is a great site to write for as well.
That said, the last thing you want to do on Xomba, at least as of the date of this article (2011), is to bookmark your own article posts. If you are writing articles on a 'get paid to write' platform or have your own personal blog, Xomba does not want you self promoting your own work via bookmarks.
I'm not entirely sure if this is because Xomba is being overrun with self promotion and they want to clean up their act, or if they know something (such as a penalty) in the works with the new Google algorithm that was recently released.
Simply put, if you write an article, just like the one I'm writing right now, and you bookmark it under your Xomba account, you are at risk of having your account suspended. That said, as of the date of this article, it is all right to bookmark the work of other people if you genuinely believe that people will find it interesting and your summary supports the article with original content. Original content is not just repeating what is in the article. For example if you were to bookmark this article (which, by the way, I'd love you for doing so,) you could not just write in your summary, "This is an article explains that Xomba no longer allows you to bookmark your own work...." etc. etc.
If you want to learn more about Xomba, I did write a review on the topic a while back. I also updated it recently to discuss some of the info above as well. I have linked he article below
Is Xomba a Scam? Nah! A Xomba Review