[freakinvibe]

To be precise, you are not cross-posting but multi-posting (copying the same question to multiple different forums). There is no way for someone to know that your question is also posted in another forum.

Cross-posting would be if you see in the headers of your post, to which forums or news groups your question has been posted (similar to the cc field in an e-mail).

Imagine, I am reading your question and I am going to answer it. It takes me ten minutes (do some research, formulate the answer etc.). In the meantime, someone in another forum has already answered your question.

Because you are happy and you got your answer, you will never read my post. I have wasted my time for nothing.

Because you are doing a lot of multi-posting, I am not going to answer your questions anymore. Your net reputation may go down because of multi-posting.

I would take knotty's advice and only post to one forum. If you don't get any answer within reasonable time, you can still ask in another forum.