The SitePoint PHP blog has a new post today sharing what they (well the author, George Fekete) see as the top 18 critical oversights common to web development in recent years. While the examples are in PHP, the principles could apply across multiple other languages.

Over the past years I had the opportunity to work on some interesting projects, complex in nature with an ongoing development, constantly upgrading, refactoring and adding new features to them. This article will cover the biggest coding oversights most PHP developers make, when dealing with medium and large projects. Oversights such as not differentiating between development environments or not implementing caching and backup. [...] The root of these problems lies mainly in developers’ knowledge and experience, especially the lack of it.

He's broken them up into three different overall types: design, application and database levels. Included in his list are things like:

• Developing with error reporting off
• Not implementing caching
• Not using automated tests
• Not differentiating between read / write queries
• Not using transactions
• No backup
• No monitoring

Check out the full post for the rest of the items on the list, all including examples and explanations.