I found that CKEditor and FCK Editor have problems with tables. If you try put table in article it will add (I think)
or

tags before table depending on how much rows you have in table. So if you have table with around 20-30 rows then you'll have biiiig blank space from text that is before table and table itself. That is the reason why I never used FCK Editor, and now I see that same problem in CKEditor.
Don't know if someone else report that before.

I tought this was only when editing with existing tables, not for the created ones.
It happened when there were new lines (or spaces?) between the various table tags as between , , , /, etc

See also this.

Hmmm. I don't see that in my installations. Remember, if you use WYSIWYG, you must turn off the "Enable Line Break" for each item. Currently, most modules don't disable that automatically when you are using a WYSIWYG editor and so when rendering it, there are line breaks all over the place. Also, for a few modules, you have to actually edit some code like the article Ghia pointed you to. You may want to look at the FCKeditor info I've posted to X.o. I'll soon be working with the CKeditor and CKfinder since that is the longer-term forward direction for FCKeditor, but not yet.