visualizing Git's Git repo

I'm a casual Git user. One thing that's been troubling me about Git is that when I look at Git's own Git repository, the revision history is not at all easy to understand. I like to view my own Git repositories with:

$ gitk --all --date-order

When I run this command, what I'm really asking is "give me a visual summary of what's up with my project lately." But with Git's repository, there are far too many branches and merges for this view to make any kind of visual sense.

So my questions are:

1. what do you all do to get a high-level view of what's going on with  
Git development?  do you use gitk?  if so, what options?

2. as a project, why don't you rebase when merging long-running  
branches into master?  For example, take commit 7e83003029 from May 25  
which merged a branch that was based at 4b172de81 from May 14.  Why  
not rebase this to May 25 as part of the merge?  When you don't do  
this (ie. in the status quo) 'gitk --date-order' for the Git  
repository has >10 parallel branches most of the time, which makes it  
impossible to follow visually.

I'm sure you have reasons for doing things the way you do, I just want to hear what they are. And sorry if this is a FAQ -- feel free to point me at any documentation that explains this.

Josh