My company bought a Synology DS 1511+ about four months ago due to our aging Thecus NAS starting to show some signs of giving up. Note that we had been using this Thecus unit for many years, and the only problem we were having was that we would occasionally get warning messages about the disks being on their last legs. All our file operations were fine.
The Synology unit has had issues from day 1, mostly to do with file locking. After several weeks of random "This file could not be saved", or "Too many open files" messages, we started to ask Synology for help. They were useless. It took over a month for them to even acknowledge our increasingly desperate pleas for help, and several times we would arrange a time for them to log into our system only for them to forget to turn up.
Eventually we started fiddling around in the system ourselves, bumping up inode limits, stuffing around with everything to try to stop the system from falling over constantly. It doesn't help that when you turn logging on, the device suffers from a memory leak that after a couple of days renders it useless. It also doesn't help that they're using a version of Samba from 3 years ago.
We're waiting delivery of a QNap device as I type this, and I seriously can't wait to see the end of the piece of shoddy crap from Synology.
Please, do not buy a synology NAS. You'll regret it later.