I did buy a small postal scale at Target (I think). Less than $20 and it is great. I weigh everything before I list it, including packaging and rounding up for label, tape, packing list, etc. I printed the postal price charts from usps.com for 1st class, parcel post and priority, and the zone chart for my zip. Then I can know exactly what it will cost. I round up for the listing to cover supplies and time, but I still keep it low. I select "flat rate shipping" and put in the cost there. Then it is my choice to do priority or parcel post etc. I print all my postage, labels & packing slips from the paypal shipping center (it does cost .13 each). Then I can just drop them into any mailbox or call for a pickup. Beats waiting in line at the PO with a 2 year old!
The so-called theory behind the Sunday ending is that more people have access to their computers on the weekend. I know many people do surf from work or late at night, but not everyone can. If they are online, supposedly they are more likely to bid higher near the end time. For example, an auction that ends at midnight on a Tuesday is unlikely to have as many last minute bidders as one that ends at 4 p.m. Sunday. It works for me but YMMV.
ITA with the PP about books - don't bother with ebay (unless you're buying); use half.com CDs do pretty well on ebay though.
Mama to 3/03 and 12/06, married to for 18 years