IPC codes can be helpful, you just need to be careful. In my experience, it's fair to say that not all IPC codes are homogeneous, or have the same level of homogeneaity (spelling?). In other words, not all the art in the same code is similar.
This is important because if you want to compare patents within a code, you need to make assumptions on how similar the patents are. For example, some statistics that you can calculate in IPC codes (and are also available on Patents360 I think ... maybe the moderator can chime in) try to identify the patents in the same code - and possible same year of publication - that have the most backward references (i.e., patents that reference them). This can be a good place to start.
For your refererence, you can lookup the full set of IPC codes here:
http://www.wipo.int/classifications/fulltext/new_ipc/ipcen.html