simplex: BASCOM AVR is superior to Arduino IDE. Bascom is simpler and much more flexible. In fact, Bascom is the language used by the majority of hobbyists.
Pretty bold statements. I think looking at google trends is a good indication about somethings popularity or relevance. Here is BASCOM vs Arduino: http://www.google.com/trends/explore#q=bascom%2C%20Arduino&cmpt=q World wide Google searches for BASCOM (not just BASCOM AVR) is waining while searches for Arduino is still climbing quite rapidly. It is very interesting to see a few BASCOM hotspots: Iran, Poland, and Indonesia The rest of the world seems more interested in Arduino. And even in those hot spots, the only one that is still higher than Arduino is Iran and even there, the search activity is declining almost to match Arduino searches.
While not exactly an indicator about what hobbyists are using for development in in their projects, clearly there is WAY more interest in Arduino than BASCOM.
Also, my concern for BASCOM is that it isn't free and doesn't have have the infinite extensibility of C/C++ It also looks like they charge for additional functionality. From their web page:
It is designed to run on W95/W98/NT/W2000/XP and Vista
That can be an absolute deal killer for some people, including myself. (I don't do Windows)
If the Arduino IDE starts to become limiting, one can convert over to Makefiles or use some other IDE on top of Makefiles and leave the Arduino IDE behind. Then things like source level debugging using gdb becomes much easier when not use the Arduino IDE. If Arduino starts to feel cramped it too can be left behind. If using Windows, Atmel has their GUI IDE AVR studio. The nice thing about staying with C/C++ and the AVR gnu tool set, is that it easy to swap out the upper level development tools for a new set of tools and not have to change the underlying AVR source code or programming language.