The days of keeping bits on spinning rust are coming to an end....
Both Samsung and SANdisk have announced 32GB SSDs. SANdisk's comsumes 0.9W max (competing disks take 1.9W) and fits in a 1.8 or 2.5" drive form factor with ATA interface. The sequential performance of these SSDs is similar to normal disks for reads, a bit slower for pure writes, but as soon as you start doing random reads or writes they are an order of magnitude faster than disks. The smaller the random accesses the bigger the relative speedup. The latest announcement from Samsung is a 1.8" 64GB version, and there is some discussion about the growth of this market in the press release.
This makes perfect sense for millcomputers. Small millicomputers can be directly connected to gigabytes of NAND flash via the SDIO interface, and larger millicomputers can use ATA interfaces to connect to flash-SSDs. The extra random performance of the SSD offsets the lack of disk spindles in a compact design and will make IO intensive workloads extremely competitive for millicomputing.
The MTBF (reliability) of SSDs is also far higher than disks. A mirrored pair of disks may be replaced with a single SSD since it has much higher reliability. This helps offset the current price premium paid for the SSD.
In the past SSDs have been built using technologies that were far more expensive than disks. Flash based SSDs have now reduced the gap, and the trend is that SSDs will eventually become bigger and cheaper than disks, the only question is when, and my answer is sooner than you think!
Update: here is a detailed benchmark review from Tomshardware.com.