At SPA2008, there was much debate amount the use of agile practices in developing software.
A comment that I heard was 'that for all the noise that the agile community makes us believe that agile is mainstream and the most common approach in developing software today, the reality is somewhat different'. Certainly there are many good examples of where agile approaches have been successfully applied but I guess that many of these are in 'young' and 'smallish' companies and not in large, corporate companies which have many decades of history.
It is not easy to convince these large and well-established companies that there are alternative ways of developing software. One reason, is often the 'process' police. Large companies, in my experience, are very keen on following a tried and tested approach, with some limited tailoring to cater for different sizes of developments.
So what are the challenges in applying agile techniques to complex systems?