I personally never use a reserve price on ebay. I simply start the listing at the minimum price that I am willing to accept and that has served me well.
Here is an example of why, as a seller, I would not reveal a reserve price. Let's say you have a car for sale that you are willing to accept $15,000 for. Let's say there are two potential bidders who want the car and they do not know what your reserve is. If they feel that the car is worth about $18,000, they will probably bid it up to the reserve prior to the end of the auction in an attempt to find out what the reserve is and then bid to nearly $18,000 near the end in an attempt to be the successful bidder. If, however they have both been told that your reserve is $15,000, they are both more likely wait to near the end of the auction and enter a single bid over the known reserve price but not nearly as high as they would be likely to bid in the first scenario.
The known reserve guarantees that you will not sell your item for less than you are willing to sell it for, but the unknown reserve price will usually bring the seller more money.