I agree - we need a tree view, because it is a mighty
widget (and the most complex). 

The Dolphin browser is nice, but too overloaded with
kiddy icons. But the navigation is wonderful.

Smalltalk MT has the same but with another nice features.
You can see all instance variables and class variables in 
a list in a seperate pane in the browser. You also see from
which class this variable is inherited.
If you click on one of the variables, the browser only 
shows methods in the method pane using this variable.
If you click on one of these filtered methods the browser
shows the variable highlighted in the source code.
(see http://www.rz.tu-ilmenau.de/~ai041/stmt1.gif)

You can also right click on a class variable and open 
an inspector on its current state via menue.

And you can drag and drop anything around in ST/MT.
For instance if you drag a method into the project 
browser this method will be included into the project, ...

Smalltalk MT also has nice features for browsing senders and
implementors. (see http://www.rz.tu-ilmenau.de/~ai041/stmt2.gif)
If you have clicked on a method in the Class Hierarchy Browser
you can select Senders, Implementors, Local Senders, Local Implementors
and Messages sent by the method. Then a new browser (shown in the
second picture) opens up and you can go on clicking on Senders, ...
You get all of that in a tree view and it is wonderfull to navigate.

This system also has a global search for word/filtered words 
which is very very fast. Searching the whole sources is very fast
but windows needs some time (1 to 2 sec) to fill the tree view ;)
Also recompiling all methods only takes 5 sec.

VisualAge Smalltalk also has powerfull tools for searching and
navigation.
(very usefull on such an overloaded system).

I think we need more tools like that in Squeak.

Bye
Torsten