I am a long time user of MJ, but am no longer sure I can recommend it to others. In fact, I believe the app may be at a crossroads right now (at least it is for me). While MJ is certainly, by some length, the fullest featured, most well established journaling app out there, much of the recently added functionality (especially that added from v. 5.X to 6.x) will not be useful or necessary to the average user looking for a simple journaling application. Power users looking for an app to help them multitask with multiple blogs/journals will likely still find MJ to be the best for their usage. Additionally, I find the interface to be less intuitive as major versions are released, as well.
There are a lot of journaling apps which have popped up over the last year or so, and at substantially lower prices (and with substantially better iOS complements and syncing). I would recommend strongly following the development of those apps before jumping in here. I know I am a feature update or two away from jumping to one of them, full time.
For those who decide MJ is for them, I would strongly urge you to purchase it from Mariner's website and not through the MAS, where updates can take a long, long time to be released. As an example, a Mountain Lion compatible version (6.0.5) was released to direct purchasers on 7/26. As of the date of this post - almost a month later - no MAS (and hence no ML compatible) version is available through the MAS (and with no word or updates by Mariner to its customers). Also, the iCloud syncing promised on this product long ago has yet to be implemented, so even if you want to buy the accompanying iOS apps, Dropbox is the only way to do so at this point, further negating any reason to purchase through the MAS.
Bottom line: while this may be the fullest featured journaling app out there, I no longer feel as though it's feature set is worthy of its very high price tag (relative to the other apps in the category), development of the other apps seems to be progressing at a much faster rate and purchase through the MAS will lead to frustration and delay on the part of the user. Recommended only for power users in need of a blogging/journaling app.