I have been trialling Synk 7 on and off since March. I have probably sunk at least a whole working week in trying get it to run. But its behaviour is still erratic and the reasons for it are close to impossible to tracking down. And Decimus has been unable to give me any help or pointers besides nice words of encouragement.
And since Synk 6 is non-functional on Lion thus have to consider Synk abandonware.

The key problem is that Synk 7 almost never manages to get my boot drive into sync, pegging both my processor cores fully for 12+ hours (the most time I can give it during a weekday).

I have spent the last two weeks again tracking down what is tripping Synk 7 up. I successively reduced the workload from 3 million, to 2 million, to 500000, to 200000, to 100000, to 20000, to 3000 files by excluding stuff. None of these managed to get into sync by running it overnight. I then went the other way around, not by excluding stuff from by boot drive but by merely syncing individual folders. That worked well and miraculously after some successive buildups of number of files under considerations, syncing the whole boot drive worked (ie, it managed to get into sync).

Unfortunately, trying it again today, there is still no sign of it getting into sync after 4+ hours. My best guess is that the rare successes I had with Synk 7 are all down to luck, ie, there are one or more processes that cause Synk 7 to effectively hang itself but I have no clue what it is. Since my computer is usually running around 140 processes (counting the PIDs), finding the offending one by trial and error is anything but trivial.

And in their great wisdom, Decimus (or shall we say Benjamin Rister) did not build-in any debugging tools that would show me which folders (or files) are causing Synk 7 to never finish, thus essentially abandoning all their customers which have a slightly non-perfect system (with Synk 7 not working and Synk 6 also not working anymore on Lion).

Of course, they say, I should just look at the list of activities but more often than not this list is empty (whether that is a sign of Synk 7 having half-crashed or 'just' a UI bug is naturally an open question). And that Synk 7 can peg my processors with basically zero disk activity for several minutes does look much more like Synk 7 hanging itself as some external process causing it to re-scan a folder.

Naturally, Decimus could give me a debug build of Synk (one that simply logs what it is doing, making it maybe possible to say where it gets stuck). But that seems outside their technical or resource or goodwill range.

Decimus has abandoned the non-live sync backup market (they market Synk 7 as a live-sync tool and have stated to have no interest in adding a non-live mode to it). As has the creator and lead developer, who has left the company.

Thus, I too should probably abandon Synk and Decimus. I am sure there is some great work inside Synk 7 but launching a new product that at same time abandones a good deal of your customer base is not something that creates a lot of trust into their product.

Thus, as a warning to all potential buyers of Synk 7: Don't feel too comfortable using it as a backup tool for your boot drive (where lots of processes constantly write files), it might stop working at any moment.

Capabilities look very nice on paper, hide the fact that it killed a previous app which had a partially overlapping set of features. So, new features have come, old ones disappeared.
Unable to complete a sync for me for my boot disk, worked on pure data drive.
Some very horrible UI elements, though also some nice ones. But the horrible ones stick out unfortunately, eg, the menu bar icon or whole lower right part with thin divider lines in a completely arbitrary relation to another.