Hmmm. . . The answers you've already gotten have 
been good. Here are my takes on the questions:

Sending: Whatever the item, I try to send it 
within a few days of receiving payment. But this 
can sometimes get screwed up by a bidder paying 
late - I might have lots of available time to 
send an item before "X date", but if the payment 
arrives after that date, I might not be as 
available. In any case, unless I'm going to be 
over a week late, I don't bother writing. (The 
exception to this is if I had made previous 
commitments to a bidder to ship very quickly - 
then I would write immediately if there were 
holdups.)

Defects: I try to be very critical when examining 
an item for any defects that will need to be 
listed. For cels, I can say that one thing I 
rarely list is line fading. I expect the scan to 
reflect that. (If it doesn't for some reason, I 
do then make mention of it.) Also, I don't note 
when cel layers are stuck so long as they're 
aligned. Anything else should be listed, 
including: misaligned layers, if the cel is stuck 
to it's sketch or background, damage to the 
cel/sketch/background, missing sequence numbers, 
missing or chipped paint, correction paint on the 
front of the cel, excessive abrasions on the 
surface of the cel, ANY trimming, ANY restoration 
attempts (professional or otherwise), and any 
creases or dings in the acetate. But everything 
like this is relative - something that one person 
might not consider a defect might be terrible to 
a different person. It kind of depends on what 
was wrong (which, as others have stated, you 
didn't exactly mention).

Selling to others on the Forum: On the one hand, 
it doesn't make any difference. But in another 
way, it's nice since (unlike with a random Ebayer)
you know *something* about your bidder prior to 
needing to complete the sale. In the case of cels 
(which seem to inspire more personal attachment 
than other items) it's also nice when you know 
your cel is "going to a good home". On a couple 
occasions when I have won Miyu cels off Ebay 
which were being sold by another Forum member, I 
was told they were glad to see it going to someone
they *know* is a fan of the show. So this last 
one is more a "your milage may vary" question.

Many Sharp Smiles,
--Drac