1. •Crippled C++ support. Symbian is C++ based—at least on the surface. When EPOC32 was designed (about 1993-1994 I think), there were very few good C++ compiler with full support for the newest C++ features like exceptions. Exceptions is the main feature in C++ for correct and efficient error handling. The other alternative is to use error codes like most operating systems use in their C APIs.
   
   Symbian chose to select neither technique. They made their own home-cooked version of exceptions called Leaves. With an exception in C++, any memory or other resources in allocated objects are deallocated automatically in the correct order (deterministic destruction by calling each object's destructor). This makes it (relatively) easy to make correct programs in C++ for both small and large projects.
   
   In Symbian when a error is signaled with a leave (‘throw an exception’) no objects are deallocated. They just leak, if you don't manually record each object allocated to be cleaned up. This process is extremely tedious, error prone and boring. The result is that it's very hard and time consuming to make correct programs in Symbian, on the verge to be impossible in many cases.
   
   C++ is a great language because of the advanced features, like exception handling with automatic cleanup (search for RAII, Resource Allocation Is Initialization), the standard C++ library (formerly called the STL library with lots and lots of support code for handling of data in containers-like lists and maps and tree structures, strings, algorithms, support for template code and last but not the least—all the standard patterns, practices and idioms all experienced C++ programmer are using on all design problems they are faced with.
   
   If you remove the foundation for standard C++ development, it all falls together. Every design decision means the programmer has to think from the ground up to make a completely new architecture for the design because the normal way of thinking and the normal guarantees C++ and experience gives, doesn't apply anymore. It really turns an experienced programmer into almost a beginner with lousy tools. It's a nightmare for both programmer and development managers. 
   
   
2. •Confusing and limited string handling. There is no real support for a proper string handling. To use strings on Symbian you have to use a home-cooked and strange system of ‘descriptors.’ Every new programmer to Symbian spends the first weeks struggling just to understand how (and why) this system works.
   
   The reason was apparently to save a few bytes on each string. But of course, today, that's not even close to being relevant. Maybe a small point but, it's yet another point that makes Symbian hard to use, hard to understand and hard to port programs to/from other platforms. 
   
   
3. •Limited support for multi-threading. An important technique used on all other platforms but is not used on Symbian. They do have limited support for threads, but it's strongly recommended not to use threads since it ‘takes to much resources.’ That was hardly even a relevant argument in 1993 but it meant that Symbian uses ‘active objects’ instead of threads in almost all applications.
   
   Active objects are just a very complicated variant of cooperative multitasking, where each object runs in sequence (unnaturally split into small subtasks) and are not able to preempt each other. It takes a lot of code to make this work, just to give the result of a system that is not very responsive, hard to program and port to/from other platforms. All for the aim of saving some CPU cycles in 1993.
   
   
4. •Bad development environment. The development environment and SDK for Symbian (S60) is very strange and difficult to use. It can take several days to just make a functional installation of the SDK and development environment. My first installation a few years ago took over a week to setup and was very fragile. On the Nokia forums there are postings with recommendations on how to make a correct setup. If you do just one step in the wrong order it fucks up. You cannot use the latest version of Visual Studio but need to install Visual Studio 2003 to make it work. But everyone that does Windows programming have VS 2005 installed. Nokia also provides several commercial alternatives, ‘Carbide,’ that is based on Eclipse etc. But it is generally a very bad situation if you compare with Xcode/iPhone or other platforms.