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    <p>Just chiming in with my experience in case you still haven't solved it or anyone else is looking for more experience. I've recently developed a pretty heavy (regular QGraphicsView, OpenGL QGraphicsView, QtSQL database access, ...) application with Qt 4.7 AND I'm also a stickler for performance. That includes startup performance of course, I like my applications to show up nearly instantly, so I spend quite a bit of time on that.</p> <p><strong>Speed</strong>: Fantastic, I have no complaints. My heavy app that needs to instantiate at least 100 widgets on startup alone (granted, a lot of those are QLabels) starts up in a split second (I don't notice any delay between doubleclicking and the window appearing).</p> <p><strong>Memory</strong>: This is the bad part, Qt with many subsystems in my experience does use a noticeable amount of memory. Then again this does count for the many subsystems usage, QtXML, QtOpenGL, QtSQL, QtSVG, you name it, I use it. My current application at startup manages to use about 50 MB but it starts up lightning fast and responds swiftly as well</p> <p><strong>Ease of programming / API</strong>: Qt is an absolute joy to use, from its containers to its widget classes to its modules. All the while making memory management easy (QObject) system and mantaining super performance. I've always written pure win32 before this and I wil <em>never</em> go back. For example, with the QtConcurrent classes I was able to change a method invocation from <code>myMethod(arguments)</code> to <code>QtConcurrent::run(this, MyClass::myMethod, arguments)</code>and with one single line a non-GUI heavy processing method was threaded. With a <code>QFuture</code> and <code>QFutureWatcher</code> I could monitor when the thread had ended (either with signals or just method checking). What ease of use! Very elegant design all around.</p> <p><strong>So in retrospect: very good performance (including app startup), quite high memory usage if many submodules are used, fantastic API and possibilities, cross-platform</strong></p>
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    1. POQt Application Performance vs. WinAPI/MFC/WTL/
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    1. COWhy use QFuture/QtConcurrent run when you have all these in C++ 11 standard now (std::future, std::async, and if you want more low level std::thread)? You will stay as portable using QT as ever.
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    2. COMy answer dates from a little bit more than a year ago, at which point C++11 wasn't even approved yet. Even now it is still not that widespread. The latest and greatest compilers support it decently but not everybody will be able to use that yet. Which is why these classes will stay relevant for quite some time and are in my opinion quite user-friendly. By the way if you go Qt you usually go all the way, which means leaving the STL by the side. But one can mix and match, of course.
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