It's good to see all the people giving Launchpad a try, and discovering both its cool bits and some frustrating bits. For those who are finding some irritations, please give it some time - when I first started using it, I also found the interface to be unintuitive in places; I'm hoping the tips and tricks I'm posting will help.
Here's half a dozen tips related to bug duping:
1. Adib asked about how to dupe bugs. This falls into the cool feature category, but the links may not be where you expect. When viewing a bug, "Mark as duplicate" is in the Actions list on the left. From there, you can indicate the bug id number that this is a duplicate of.
2. The bug report will clearly tell you that there are dupes of a given bug, or that the bug is a dupe of such-and-such other bug. For bugs with dupes, there is also a listing of its dupes - this can be found on the left column in an expando-box titled "Duplicates of this Bug".
3. When a bug is marked as a dupe, it no longer shows up in searches, which is nice. But you can still get to it either directly by ID, or via the link in the parent bug.
4. People who were subscribed to the dupe bug will now receive the update notifications from the parent bug. This is usually useful, but keep it in mind if commenting on a bug with a large number of dupes that you're not spamming everyone with trivialities.
5. Note that it's not possible to mark a bug a dupe if it also has dupes attached to it. You have to individually move the dupes to the parent. Sort of annoying, but it's rare when you need to do this.
6. When closing a bug that has dupes, it's good practice to review each of the dupes and check that the solution definitely does account for all those reported problems.
I was at first annoyed to find endless duplicate reports of bugs, as it seemed like a waste of effort that could be avoided if the reporter searched the existing bugs. However I've since changed my mind, for a few reasons. First, (at least for xorg) most users don't have enough knowledge to really know for certain that their problem matches someone else's, so it usually requires an expert to verify that the issue really is a dupe. Second, from a workflow perspective, finding/marking dupes is much more straightforward than trying to untangle a bug report that contains multiple unrelated issues in it. Third, a bug report with a lot of dupes typically ends up being easier to gain a fix than one with no dupes - both because it emphasizes the importance of the bug, and because the "many eyes" effect starts kicking in, and people subbed to the bug through dupes can start sharing ideas and findings with each other.
So, I generally encourage tell reporters, "If you're concerned that your bug report might be a dupe but you're not sure, report it as a separate bug, and just say in your report 'might be related to bug xyz'". This saves the bug triager time of tracking down potential matches but still lets your issue be handled even if it's unrelated.
Bryce