Yes, you can put macros in any workbook and have the icons on any toolbar
assigned to any of those macros.

But that becomes very difficult for organization purposes.

If you have macros that you want to make available to others, then put them into
a workbook, but don't save it as personal.xls (or personal.xla).  

You can only have one workbook open that has the name of personal.xls and if any
in your audience is already using personal.xls for their own stuff, it'll cause
heartache and pain.  They'll have to decide to keep yours or keep their own.

Instead, you can use a different name (MarcoUtils.xla, saved as an addin).

You could build the menu by using John Walkenbach's menumaker program:
http://j-walk.com/ss/excel/tips/tip53.htm

Then you can share this addin in a couple of different ways.

If each user always has access to a common network folder, you could put it in
that folder and tell the users to install it via:
tools|Addins
and browse to that folder.

Then you have one file to keep up to date.

If the users don't always have access to that folder, you could send them the
.xla file and tell them to save it to a nice local (C: drive) location.

Then use tools|addins to browse for your addin.

If you're really industrious, you could even give them a small installation
program that they run to install the addin.

Jan Karel Pieterse has a nice install program included in the .zip file for his
(with Charles Williams and Matthew Henson) name manager utility.

You can find it at:
NameManager.Zip from http://www.oaltd.co.uk/mvp/

And if you use names in any of your workbooks, keep that name manager utility.
It's very helpful.