I've been trying to decide on the same models.
the 3109 or the s530d. I'm going w/the s530d I think. I've heard more bad about the toshiba than the sony. At least the newer sony models are fixed. I heard the toshiba remotes were a bitch.
Here's some stuff I found on audioreview.com

SONY SERIAL NUMBERS To AVOID: 0100001 - 0119840
0800001 - 0953000
10001 thru 119840
80001 thru 953000
You can find the serial number on the outside of the box by locating a barcode sticker on the side of the box (usually). At the bottom of the barcode itself will be a number that starts with S01#######. The Number following the S01 will be the serial number on the back of the unit. This is also the bar code label that must be sent in to cliam the 5 free cds. To find a MANF DATE, look on top of the bax, there should be a label with a bar code and a date at the botton like: 11/12/99. This should be the date it ws shipped from the warehouse.