Salesforce is a rather painful experience for developing anything but the most simple applications. Salesforce has a very specific idea of what one would want to develop, and if your application isn't well within those boundaries, steer clear!
The governor limits are really quite pitiful: 16 level recursion, 1 meg heap, no more than 200 objects returned from a query, no more than 20 queries in one invocation. 10 web callouts in one invocation, 1000 items in a single list, and they go on. The ultimate result is that any cleverness you come up with to get around one limit runs afoul of another one.
Once you reach certain size, all your time will be spent on coding around these limitations. The language, Apex, doesn't really support any meaningful inheritance. Even seemingly simple tasks end up taking days when one encounters new and apparently arbitrary limitations, for example, all objects in Apex inherit from SObject; however, it is not allowed to instantiate a collection of generic SObjects, making it all but impossible to build useful utility libraries. Complex (even rather simple) database joins are not possible.
The tooling and support for Salesforce are also extremely weak. They are untrustworthy and difficult to use for real development processes. Deployment is a nightmare, since the tools have enormous difficulty working out complex dependency issues, and numerous entities that one will create in the course of normal development simply CANNOT be deployed programatically. Other little features are delightful as well, such as the fact that the language is case insensitive, but the IDE is case sensitive. There are no refactoring tools to speak of, so you get all the pain of a statically typed language, with none of the purported benefits. And the save/compile time is high- I see times of over 2 minutes with frequency. And, of course, if you have multiple compile errors in one save (and you will, since you won't want to be recompiling every change, with those 2 minute waits...) you'll only get one error at a time!
On a related note, you seem to have noticed that the Salesforce documentation is rather self-congratulatory-- well, it's like that ALL the way down. There is no mention anywhere in even the most deep-dark technical references of the common errors, or even the limitations of a given api or feature. It's all "here's the great thing you can do" and no mention of, "but you would imagine it would also do ___, but you'd be wrong! Dead wrong!" The documentation truly feels like marketing material all the way down. I've been programming in this environment for 18+ months now, and still occasionally have a hard time finding basics, like API reference.
Salesforce is not a flexible environment. It is not a rapid-development environment (at least compared to any other web-programming framework out there). It is not a good environment to build anything other than toy applications like those they show in their tutorials. Just say no.
