Never contact people in person to ask a question unless they have explicitly given you permission. Even if someone was kind enough to reply to a previous question, this doesn't mean he wants to be your go-to person for every subsequent problem as well. If you do this, don't be surprised if your question is ignored. Just think about how many emails these people receive daily, and you will understand the reason. Remember that this is a voluntary effort, not a technical support service.
If a reply to your question is posted to the list and you want to follow up on it, in most cases you should keep posting to the list, so the conversation will be saved in the mailing-list archives and can later be reused by other users who seek help in the archives.
However, if you receive a private email reply to the question, keep the conversation private, because the person who has answered you might not have wanted his answer to be seen in public. You have to respect that and not resend the reply to the list without this person's permission.
When posting to the list, always use relevant subject lines. Don't just say "help" in the subject field of your post. Chances are that these messages will be ignored. Most of the people are interested in only specific topics, and therefore they will delete messages with unspecific subject lines without even reading them. To catch their attention, you should provide a concise, meaningful subject line.
When replying to a message, please try to quote only relevant parts of the original post: don't overquote and don't overtrim. Refrain from replying on the top of the original message, since it makes it hard for other users to understand the conversation. Please use proper quoting delimiters, so users can easily tell your reply from the original message.
If your English is not fluent, do not feel frightened to post. The mod_perl community includes many people for whom English is not their primary language. But please run a spell-checker before posting if you know that you tend to make many mistakes. Sometimes people post questions that are never answered simply because nobody understands the question.
Avoid posting off-topic (not mod_perl-related) questions. If you really feel that you have to, at least let others know that the post is off-topic. The correct way to do that is to start your post's subject field with the [OT] tag.
Avoid flaming. At least, don't flame in public—contact others in person if you really want to. Flaming people in public may hurt their feelings. They might leave the list, and all of us will lose an active (or potentially active) contributor. We try hard to make the mod_perl list a fun place to be.
Remember that sometimes it might take days or even weeks before your question is answered, although during the working week most questions are answered within a few hours. Occasionally, questions aren't answered at all. If this is the case, you might want to post again some time later (at least one week), maybe with more information.
Finally, use common sense when posting, and you will be fine. Online conversations needn't be any different than real-life ones; be polite and precise and everybody will be happy. Subscribing to the list and spending some time reading the posts will give you an idea of how things are done.