I definitely like having our eBay store. On items sold, eBay costs are similar by the time you pay the higher final value fee. But for the items that you list in the auctions and don't sell, they can eat away at your profits on the ones that do sell. With the store you can list your items longer and the ones that don't sell don't cost so much. You can list an item in the store with a gallery pic for a year for $0.36. Much better place for slower moving items, or those items that take a little longer than 7 days to find the interested buyer. Use things that you know will sell easily to list in the auction to advertise and bring people into your store. I've read quite a bit on the stores discussion board at eBay, and most people tend to say that you should have about 100 items listed in your store to make it worthwhile. There is quite a bit of good info at the stores discussion board, but keep in mind there is also a lot of negativity, so if you check it out, be prepared to dig the gems out of the dirt and not let the negativity affect you!
PS...you can also get a domain name and have it redirect to your eBay store...advertise it everywhere you can!