A few answers:
Crossposting is frowned on because it wastes people's time. The people who answer questions here are volunteers. They also will often belong to one or more forums, so if they see a question cross-posted elsewhere without indication that it is a cross-post, they will most likely (1) be upset if their effort has been wasted and (2) unlikely to answer anything else that you post, here or on any other forum. At the very least, let people know that you have posted the same question elsewhere, and provide the link.
There are many reasons why a post doesn't get answered quickly. Often, it's because the post is not clear and people can't work out what is needed. In most cases they will move on. There is a post in the Board Announcements with some helpful tips:
http://www.mrexcel.com/forum/board-announcements/685723-help-us-help-you.html#post3393381. Take time to present your question properly, and people will take a look and have a go at answering. Note: DO NOT oversimplify. If you ask something simple, get an answer, and then respond with something "thanks, but what I really need is [insert something much more complicated here]", you will lose your readers.
This Board moves quite rapidly so your question may disappear from the front page a few minutes after posting (in peak times). If you bump your post, there are some potential problems: (1) Do it too fast, and people will see you as impatient and possibly ignore the post. (2) A lot of people search unanswered posts to see what interests them. By bumping the post, you miss out on those searchers finding your post. (3) If it really is taking a long time, take a look at the earlier paragraph. I would wait at least a few hours before considering bumping the post. If you can't wait that long, and you need something more complex than a volunteer can handle in thier spare time, consider paying for it. MrExcel Consulting covers a wide range of work.
Hope that helps
Denis