On the current version of OS X Snow Leopard (10.6.8), I have an icon sideways on my desktop:
Any idea why or what it signifies?
It's not that the icon is sideways, it's that the small thumbnail for the file that's used as the icon needs to be wide because the CSV file has at least one really long line of data in it. The thumbnail you're seeing is a dynamic preview of the contents of the file and in the case of the file on the top of the image, the data contents demand a lot of horizontal space to show you the preview.
Here's an example: I've created two CSV files on my desktop. One file has ~500 columns of data on one row. The other has 10 columns of data on one row. The thumbnail for the 500 column file is wide because that's what previewing the data demands.
Pretty smart of OS X really.
Edit: Someone asked where the threshold for change was in the thumbnails. I did some quick experiments. I saw changes in the thumbnail dimensions at 61, 81, 101 and 121 characters of text on the one line. Note: that is characters, not columns of data. So it includes the data and the separating comma. Here is how the thumbnail icon evolved as the file contents changed:
For all of these snaps I just changed the length of the text on the one line in the file via TextMate and save the file, viewed my desktop and there was an updated thumbnail.