Gary King has been working on getting a good library system for lisp, and recently posted his Notes on a Lisp Library Management. I was going to email him back, but figured here was as good a place as any to give my comments. Read that first.
Firstly, I applaud Gary for taking up this mantle. I'm really still starting using lisp, and the lack of authoritative libraries is a hinderer for people like me. Getting a comprehensive library management system is going to help folks like me get up to speed with lisp faster. ASDF is a good start, but I think it needs to be built upon. Secondly, sorry if everything I'm saying here has already been considered.
The problem of getting libraries installed and updated with minimal user effort is a very studied problem with several decent implementations that could be used as starting points.
I think a lot of lessons can be learned by studying perl's CPAN. CPAN has mirrors that automatically sync, and each user picks a list of mirrors near them. Then you just ask for the package name, and it will download, make, run tests, then put the code in a proper system or user path such that programs can import the library. Perhaps a port of CPAN would solve most of these problems.
Another good example could be Debian's apt-get. I think it's command line interface almost perfect, and since many lisp developers are using debian based sytems, the interface would be very familiar. As a client of a lisp library management service, here's what I think would be ideal, presented as a mock shell session (with user input in bold):
~$ asdf install clsql
Looking up definition for package clsql... package found.
GPG key not present, downloading from https://www.b9.com/kevin.gpg.asc... done.
Downloading clsql from http://files.b9.com/clsql/clsql-3.6.1.tar.gz... done.
Checking signature for clsql-3.6.1.tar.gz... file verified.
Checking dependencies...
clsql depends upon uninstalled package uffi, install uffi? [ynaq] y
Looking up definition for package uffi... package found.
Downloading uffi from http://files.b9.com/uffi/uffi-1.5.13.tar.gz... done.
Checking signature for uffi-1.5.13.tar.gz... file verified.
Checking dependencies... done.
Dependencies met.
Building uffi... done.
uffi (1.5.13) installed.
Dependencies met.
Building clsql... done.
clsql (3.6.1) installed.
~$ asdf upgrade
Scanning installed packages.
Checking clsql (3.6.1)... up to date.
Checking uffi (1.5.13)... up to date.
Checking my-unversioned-lib (20060503)... outdated!
Looking up definition for package my-unversioned-lib... package found.
Downloading my-unversioned-lib from http://example.org/my-unversioned-lib.tar.gz... done.
Checking signature for my-unversioned-lib.tar.gz... file verified.
Checking dependencies... done.
Dependencies met.
Building my-unversioned-lib... done.
my-unversioned-lib (20060526) installed.
Upgrade complete, 3 packages processed.
1 package upgraded.
2 packages up to date.
Anyway, enough pipe-dreaming for me.