I worked on (and administrated) AccuRev for more than a year lately, and most of my impressions are very good.
We evaluated it alongside with "Plastic SCM", SVN and "ClearCase-UCM" (that we already owned and used), and decided to dump ClearCase and SVN (both were used in two different groups) and to purchase AccuRev.
First, the stream architecture is much more solid, easy and safe SCM method than the old branching architecture that all the other tools are tied to (yes even ClearCase's "streams" are eventually a wrapper of branches). There's a lot of articles about the differences in their site, you can search and read about it to make it understandable. (Try this link, and this one too)
The timesafe architecture - you can't delete anything from the depots (=repositories) database. I saw tools that this operation is possible with the proper admin permissions. In AccuRev you will use internal commands in order to change or fix a mistake you made, which in turn will be recorded as a new transaction also. Very smart very safe.
integrations! AccuRev integrates with so many tools (to give you ALM bundle) - bug tracking tools (like JIRA, ClearQuest), IDEs, testing tools (quality center), and if you can't find one you can write your own (they provide Java/Perl/XML/CLI SDKs)
Change Package, I don't know about you, but I can't stand SCM tools that doesn't supply change management (did anyone said SVN?), like ClearCase "activities", and AccuRev's "issues". It's a must for my opinion, and one of my CM "best practice". And they can be integrated with your bug tracking tool too, so your users can work on real tasks like features and defects.
the support is just amazing. As a former client of IBM (because of Rational ClearCase is now part of IBM), the shift to AccuRev was simply awesome. During the evaluation they gave numerous on-line support to understand how we want the tool to act for us, so we tweaked it together even before we payed a cent. And they kept that degree of responsiveness after that evaluation period too; We had some problem during an upgrade from 4.5.4 to 4.6, in just a couple of hours (while the upgrade is still in process) the support guy contacted me back, suggested a few tips, connected to my desktop and finally fixed the problem before any other company's support would even started to try to figure who you are. Of course that if you choose open source tool than you're on your own!
Also the tool comes with help system, which can be even too verbose sometimes. And don't forget the forums (especially on cmcrossroads) that are very good in supplying rapid answers too.
And there's so many more....
Of course there are also drawbacks (which software is perfect?) - I would like, for example, to see the file(s) <-> issue(s) association during check-in too, like in ClearCase, not just in "promotion" like it is today - but IMHO they are really minor.
So, as you can understand, if you read it all, I'm a big fan of AccuRev, and I'm highly recommending it. IMHO, it is today one of the best SCM tools you got the chance to work on; modern, wise, easy and strong.
