I am using Google Documents for text editing and generally it works quite well.
However I've found, that table support is very limited.
I've switched to Google new spreadsheet and done my table quite easy.
Finally I've pasted Google spreadsheet into MS Word(it also was copied as plain text),in MS Word converted text to table, then copied the table from MS Word document and posted it to Google Document.
It is a long way to copy table from one Google application to another with the help of MS Word.
I've reported the problem http://www.google.com/support/forum/p/Google+Docs/thread?tid=78095efa3f482655&hl=en but I do not expect an answer.
It's funny that Google Docs Known Issues are listed on 1 small page (only 8 known issues.