I agree with many of the above reference annoying web-gimmicks. However, I must admit to using one of them quite liberally on our web page; Rollovers. I think a little flash (lower case "f") for the visitor with a high speed connection is a good thing. A text rollover saves space and IMO, looks crisp and professional.
On our page, when the potential customer mouses over a picture of one of our watches, the pic goes to a 60% transparent and provides price and brand info. over it. Please see for yourself and let me know what y'all think --
www.antiquewatchco.com/html/american.html --
Now, all that being said, I did not do any of this on the front page, and offer 2 different directions for the visitor to go in order to view our inventory, based on their connection speed. The dial-up page consists of small single images and text written under each image.
The gimmick that makes me the maddest... mouse trails.