Are you an eBay addict?
Not at all, but I'm probably on there 3-4 times a week, depending on what time of the month it is (payday-wise!)
Do you buy and sell or just buy/just sell?
I buy more than I sell, but I have been known to punt a few items I thought might make the queue in the Post Office worthwhile.
How often?
Buy monthly at least
Sell... 2-3 times a year? I always seem to log on just after a free listing weekend though - grrrr.
Do you pay attention to shipping costs?
OH YEAH!
When looking for Buy It Now items I always use Lowest price first (inc P&P)
I need to know the bottom line and with unhealthy mental arithmatic I can be fooled.
Do you eBay when drunk/other other influences?
Have done. Back when free time usually meant drunk.
If so, does this lead to stupid decisions?
Has done. But all bidding decisions rather than Buy It Now ones, so I've woken up and thought "Oh Shit!" then been so happy to find I've been outbid!
Do you watch your "rating" like Lumberjim used to watch his post count?
I used to. The first few stars are closer together. I think I have to buy thousands more items to get my next colour change so I'm haven't bothered for a while.
Have you any eBay purchase regrets?
Yes. Not huge regrets because I don't buy expensive items. But there have been some things sufficintly vague in their description that have arrived and I've thought - ewwww. Wouldn't have bought that if I'd have seen it! Examples - skirt described as Long that was calf-length (no measurement given) my miniscule jam tart cutter (again, no ref to size) a hideous dress that I assumed was cotton from the pic, a League of Gentlemen book I already had - they'd just taken off the dust cover (it was different underneath) and called it rare. I still got it for pennies, but it made me cross all the same. The scoundrels!
This is over many years though.
Do you ever buy things just because they are bargains,
then found a need for them?
I'd say never, but I have a nagging feeling I might have done, once. I have bought things anticipating a vague need I suppose.
Do you browse or search for specific things?
Search in a browsing way? I will often browse clothes in my size simply to see what is out there. Ditto shoes.
Do you watch s&h costs and mentally include them in the price?
S&h is a mystery to me. So I guess I don't. If you could please respond and let me know?
What's you best bargain ever?
I shop by price on eBay, so there are too many to mention. I've often been complimented on items of clothing that I've bought for under £5 (which includes P&P). Far lower than Sales prices. In terms of saving money? Probably for Mum & Dad where I've shaved off about £5 from a High Street Retailer or Amazon.
What's your worst disaster ever?
Dress I bought with a view to wearing it at my bro's wedding. It was the viscose thing mentioned above; the colour was not accurately represented and it clung in all the wrong places. It wasn't ruinously expensive, but more than I would usually pay for a dress (being a wedding and all!) and I was just so disappointed that it looked so good and was really quite nasty. That was over a decade ago now 
What is your most "unusual" purchase on Ebay?
Laser Eye Surgery - the story is on here somewhere.
Do you buy used or new or both?
Both. Mostly Used for clothes, shoes, books and DVDs, but New for cooking items, books, shoes (there is overlap). Obviously New for underwear!
Do you "subscribe" to particular vendors?
No
Do you use an automatic "sniper" to bid for you?
Not really sure what this means, which must be No.
Do you use eBay as a price index for purchases elsewhere?
Yes and No. I check a number of websites for things like books and DVDs, including Amazon (2nd hand), play.com (new) and CEX (both). CEX is a High Street store that buys and sells DVDs (amongst other electrical items). You can usually buy lower at CEX and sell higher on eBay.