I was of much the same mind, until I started doing the maths on hardware RAID 5 and power consumption.
In the end, it was a bit of a no-brainer. The DS-410j I eventually bought can be had for €275 ex drives. Chuck in a pair of WD Caviar Green 1Tb drives in RAID 1 and for about €400 I had a 1Tb NAS which draws peanuts in terms of power consumption when compared to a 'real' PC.
One comment worth making is that e.g. the WD Caviar Green drives run into trouble with Linux systems (including the Synology boxen) because of their habit of unloading heads after a fews seconds. This is not trivial for the average home user to solve (requires hanging the drive on a PC, booting to DOS and running a WD command line utility)