Only a few years ago, SCSI drives used to be far superior to IDE models. People who needed high data bandwidth, low access times and large capacities had to pay the SCSI-premium, because IDE-drives of were significantly slower and smaller.
Today the picture has changed. The advances in the IDE-sector have been so vast that nowadays the largest hard drive is an IDE-model and the fastest IDE-drives are only marginally slower than the fastest SCSI-drives.
It comes to no surprise that SCSI has finally disappeared from the home and office segment. IDE hard drives are offering excellent performance, large capacities at a very reasonalbe price. SCSI is a lot more expensive and complicated to set up, while hardly offering any benefit to the home or office user. Quality IDE or ATAPI components can easily live up to his expectations. IBM and Maxtor are shipping fast and huge UltraATA/100 drives, Plextor provides an excellent 12speed CD writer with buffer-underrun protection system, and IWill, Promise and others supply IDE RAID-controllers.
Still SCSI has still got its advantages over IDE. Large RAIDs are one example. Then you can connect 7 or 14 devices to the SCSI-adapter, like CDRWs, Scanners, of course hard drives and more. However, due to SCSI's price premium most people will prefer USB-connections for scanners, IDE-RAIDs and even IDE-CDRWs today.
Times for SCSI are hard. Most hard drive manufacturers are focussing more and more on IDE drive development. It has become difficult to develop SCSI components that are significanty better than IDE products, especially if the developer wants to meet reasonable price points.
At this point we are seeing a clear split. SCSI has died out in home and office computers. However, it is still the one and only high-end storage platform. It offers best flexibility due to vast drive arrays, teraByte capacities, cache controllers and hot plugging capabilities. This cannot be provided by any IDE system ... yet. SCSI is still able to provide a lot more than IDE - at astronomical prices.