CESCO  Nice app in conjunction with Isolator as someone has already said. What IMHO this app is still lacking are some of these features:

* Log the time spent concentrating, so you could know exactly how much time you have spent on a particular project; since Concentrate have already a built-in timer, I think that it would quite easy to write this time on a text file / CSV file / XML file. It would be a useful feature for any worker that makes invoices and bill in hours of work.

* The ability to import and export all the preferences and the blacklists

* (If possible) the ability to show a customized message when I try to visit a blocked website, something like: "Concentrate is actually blocking this website"  
(Version 1.1.1)

JACKV  I think concentrate lives up to its full power when combined with Isolator (IMHO better than things), and SelfControl or Freedom for blocking websites. Freedom blocks everything, SelfControl allows you to edit a blacklist which can be easily expanded.

I don´t think that it is a bad thing that it takes some time to setup: People that need that kind of app (like me) really don´t think about their workflows. this app pushes you to think what you really need for a given task. If you don´t take the time to do that, you can save the money as you won´t be satisfied with the app. But that´s not the apps fault.

EDIT: I forgot to rate my review earlier.  
(Version 1.1)

STILL_SPARKLING  Yikes! Sorry for writing a novel down there.

My mini-review: Concentrate has a labor-intensive setup process which hampers its utility. In my opinion, it goes about things the wrong way. Instead of making the user choose which apps s/he want to run, a much quicker option would be to have everything dis-allowed upon startup and let the user chose which apps or websites to run by checking them off a list all at once, rather than scrolling down a long window and adding them one at a time.

Nice, clean GUI except for the giant white background window and tiny fonts.

Generous 60 hour demo.

Ultimately too expensive when superior free apps like Think are available.  
(Version 1.0.2)

STILL_SPARKLING  Concentrate has a clean and simple UI, but there are a few problems that keep it from reaching its true potential.

-Setting up blocked apps and websites can be a chore because you can only pick one app/site at a time. When choosing websites to block, you must manually enter the names of each site from memory(!), one at a time, rather than multi-selecting a group from your bookmarks. A program such as this really should have a streamlined selection process; as of this version, Concentrate does not.

-The same annoyance is true of blocking unwanted apps: you must add them one at a time from a dropdown list and every time you finish one, the window closes and you must start over again. The window is also annoyingly small (so you have to scroll to see all of your installed apps); you can resize it, but it doesn't remember the larger size, so why bother? A better solution would be to have an open window showing all installed apps and letting the user put a check mark by the apps s/he would like to have open.

- A default group containing frequently used apps like TextEdit, Dictionary, and the user's default music playing app would be nice to have setup immediately after install. You can make such a group yourself, name it "Default" or whatever, and duplicate it repeatedly from within the app, but it's a tedious process due to the abovementioned annoyances.

-There should be an option to block all websites completely instead of just individually. Such an option would come in handy when you want to work with files on the network, but also want to prevent the distractions of browsing online.

-If you run Little Snitch, there will be interruptions every time Concentrate asks permission to access the network. This is especially irritating if you have apps that insist on phoning home to check for updates every time you open them, like the satanic Adobe updater.

-The desktop is not blocked out; Writeroom and Think perform this function automatically.

-When the timer finishes, an eye-searing white screen drops down to inform you that you are done. There is no way to change the color of this white background window, so the interruption is abrupt and unpleasant.

-GUI is too small for users running high resolutions on large monitors. Non-adjustable font sizes.

-Too expensive, especially when apps like Think and J-Dark are free.

Despite all, I think Concentrate has real potential, especially if it fixes the problems I mentioned above. One area where it could be useful is as a program that forces you to take breaks (by locking down the entire computer for a few minutes), or as an app that keeps you on task when you need to do a single activity, like exercise. Concentrate could play your pre-loaded dvd and prevent you from doing anything else until your 30 minutes of working out is complete.

For multi-task activities though, I prefer Think; it's more elegant and seems to flow more smoothly than Concentrate when switching between apps. However, I do really like the timer implementation in Concentrate, so I'll be keeping an eye on it to see how it develops (and if the price drops).  
(Version 1.0.2)