<p><a href="http://en.wikipedia.org/wiki/Aspect-oriented_programming" rel="noreferrer">AOP</a> is an interesting programming paradigm in my opinion. However, there haven't been discussions about it yet here on stackoverflow (at least I couldn't find them). What do you think about it in general? Do you use AOP in your projects? Or do you think it's rather a niche technology that won't be around for a long time or won't make it into the mainstream (like OOP did, at least in theory ;))? </p>

<p>If you do use AOP then please let us know which tools you use as well. Thanks!</p>

We used aspectJ in one of my big projects for quite some time.  The project was made up of several web services, each with several functions, which was the front end for a complicated document processing/querying system.  Somewhere around 75k lines of code.  We used aspects for two relatively minor pieces of functionality.
First was tracing application flow.  We created an aspect that ran before and after each function call to print out "entered 'function'" and "exited 'function'".  With the function selector thing (pointcut maybe?  I don't remember the right name) we were able to use this as a debugging tool, selecting only functions that we wanted to trace at a given time.  This was a really nice use for aspects in our project.
The second thing we did was application specific metrics.  We put aspects around our web service methods to capture timing, object information, etc. and dump the results in a database.  This was nice because we could capture this information, but still keep all of that capture code separate from the "real" code that did the work.
I've read about some nice solutions that aspects can bring to the table, but I'm still not convinced that they can really do anything that you couldn't do (maybe better) with "normal" technology.  For example, I couldn't think of any major feature or functionality that any of our projects needed that couldn't be done just as easily without aspects - where I've found aspects useful are the kind of minor things that I've mentioned.