My view on ORMs
Via Hacker News, I recently read ORM's hidden cost. As you might guess, I have an opinion on this.
First off, I agree with the article; ORMs have problems. Among other things that the article talks about, there are fundamental mismatches between the object oriented approach and the SQL approach to a problem. But ultimately the issues about ORMs are a lot like the SQL hairshirt issues: they matter in theory but they do not matter in practice to most people.
Despite all of these issues, ORMs work great at a small size and a small size is where almost all web applications live. Private and internal web apps are almost invariably small, and many public web apps will never grow very big. What matters in this domain is fast and easy development, which ORMs deliver handily because they give you a database that you don't have to think about or learn.
(Many people in this area would be just as happy with an object store that they could query. Really, that's what they're using SQL for.)
(You can worry about these issues in advance if you want to, and I've done so sometimes for web applications (DWiki is one example). But it will probably slow down your development unless you're pretty familiar with the easy best practices in this area, familiar enough to do them by reflex.)
This implies that the first thing you should do when you're thinking about using an ORM is estimate how big a database and how active a web app you're likely to wind up with. Of course you should be doing that anyways, because it'll tell you how much you have to care about all of the SQL hairshirt issues.