$600 (well, $525 now, apparently) for a 256GB top-shelf SSD is, indeed, cheap. Considering they don't get any cheaper than that right now.
In terms of compared to disk-based storage, yes, $2.05/GB is far from what you could be paying for storage in general. For instance, 2TB 7200rpm 3.5" hard disk drives are down to $0.045/GB. However you could have an entire 2U or 3U rackmount array of 15000rpm 2.5" hard disks and not see the sheer I/Ops throughput of a top-shelf MLC SSD. Transfer rate? That's different, but for low-latency seeks and high IOps, SSDs are undoubtedly king.
The best middle ground are 2.5" hybrid drives like the Seagate Momentus XT which is only about $0.24/GB now. Much faster boot, quicker wake from sleep/suspend, quicker app launches. However for data that isn't in the SLC cache, an SSD annihilates it.
The 27" iMac dual setup (SSD + 3.5" hard disk) is very hard to argue in general, and if you want more storage, FireWire 800 is "good enough" if you need raw space and good transfer rates for large files.
But yes, $2.05/GB for now is "cheap". I'm looking forward to when it gets to more around $0.85-1.00/GB, and we can grab 600GB devices for ~$500. A combination of that and the new 3TB 3.5" 7200rpm drives would make a great baseline configuration. We should be seeing 400GB and 600GB MLC drives being common from Intel in the 2nd half of 2011.