Another of the threads where people are helping others find the right NAS for their needs is over at http://arstechnica.com/civis/viewtopic.php?f=11&t=1223281#p25610075. This thread has some good discussion of Synology vs QNAP vs Drobo. A particularly interesting post is this one where the writer compares two different Synology NAS devices and states exactly what the "j" means in several Synology product names:
I have two Synologies (a DS411+II and a DS211j), and I love both of them. One caveat is that the "j" tacked onto the model number usually designates a lower power processor and smaller amount of RAM which could affect the performance of any apps you might install. Network throughput shouldn't be an issue though. Case in point my DS211j comes with 512MB of RAM and a Marvell processor, IIRC. The DS411+II is an Intel proc with 1GB of RAM. The 411 can run any of the installed apps pretty well while some will bog down the 211j, e.g. running nzbget and unpacking rar files, and sometimes slow down the interface. I've had the 211j for a couple of years now, and I've been very happy with it. I grabbed the 411 last year and have had no issue with it at all, other than the fact that I'm running out of space.
The "j" designation in Synology NAS boxes indicates that the model has a lower power CPU and less RAM than the other NAS with the same number.