You are new here, would like to comment but you don't have the privilege? If it is not on your question, it's probably not that urgent. So be patient, star the question to find it later, follow my way to earn your first hundred points and you will have the chance to properly comment soon.

Ubuntu is just one of the topics here, [there are many others][1]. You already know something about some of the topics, don't you? Pick some you are interested and/or proficient in, read their introductory [tour] to learn the basics and then just lurk around and answer wherever you can help. Odds are good that you will get 200 rep in few days, which will give you 100 point in any other site, including AskUbuntu. This will enable to [chat, ask/answer in meta, upvote and... comment!][2]

Then it's the time for the delayed comment to celebrate your reputation gain.

Final pro-tip: some sites are easier to get reputation than others. Hobby-related topics are easier to get into and new sites (no special icon, just the default blue one) means more time to answer before someone else does and more good questions waiting for you to ask. Also, watch top questions in the right pane - sites whose question appear there often are the ones where users tend to upvote a lot.


  [1]: http://stackexchange.com/sites
  [2]: http://askubuntu.com/help/privileges