I've been a user of Debian's apt-get package manager for nearly as long as I've been serious about computers, and I love it. Going back to a system that lacked apt's depth and stability would be like having to write with my non-dominant hand or worse—going back to typing on a QWERTY layout. I have seamless access to everything I need, and it never breaks unless I do something crazy like add unsupported third-party repositories or run the unstable distribution. Who could ask for more? So I'm quite proud to see Leiningen getting packaged for Debian with lots of help from the Java Maintainers team.
It's interesting to get a look inside the sausage factory of packaging. The biggest hurdle for me as I was learning the ropes was that all the packaging introductions assume you are building a C program and have familiarity with makefiles. You can tell that the packaging culture has its roots in C, and packages from other runtimes feel a bit foreign. Even more so with a language like Clojure... you're off into unexplored territory, blazing your own trail.
The biggest change from what I'm used to is the notion that only a single version of a package can be installed at a time. I think I understand the motivation here: it's crucial that when a security vulnerability is reported the affected packages and all those that depend on them have access to the fix. I'm used to developer-focused package managers that allow many versions to be installed side-by-side, but that places the burden of security updates on the developers using it since it's common for packages to depend on exact versions rather than allowing bugfix versions to sneak in. It's a lot more work to track down security issues, but this is not a big deal in the context of developer-centric systems since these particular users are less likely to mind having to pay attention to that sort of detail; it's what they're paid to do.
So there's a real tension here; end users want packages to just work and be safe without thinking about them while developers demand repeatability and control. Developers need the flexibility to choose exactly when they want to pull in new versions of libraries, while end users want things to hum along out of sight.
The problem is that the one-version-of-a-package-at-a-time policy doesn't always work in practice. Over time backwards compatibility is the exception rather than the rule; in many cases there simply is no substitute for having multiple versions of a package installed simultaneously. And apt's answer here is just to create a new package with the incompatible version number as part of the package name. There's no clue that these packages are related, and upgrades won't pick the new versions up. This is quite a shame, because I love everything else about apt. I look at complicated production deployment schemes and think to myself how much simpler things would be if deploying were just a matter of adding our internal apt repository and running apt-get install, but... versions.
Of course, these gripes are not really relevant to having Leiningen in Debian. Users of Debian-based systems will be well-served by getting Leiningen through their OS, and once it's on their system, they're free to use it to solve their developer-centric problems. This plays to the strengths of each system, and everybody wins.
Update: Leiningen has been accepted into Debian.
 Except Emacs; that's the only thing I still build myself from source. Though http://emacs.naquadah.org looks like it delivers perfectly passable builds of 24 if you're not interested in any of the experimental branches.
 It's especially noticeable with Ruby and the JVM. Part of this is due to the fact that the JVM has only been free software for a relatively short period of time, and a lot of the existing culture around Java distribution goes against the grain of repeatable builds by ignoring source and shuttling binary bytecode around everywhere.
 And it's looking like it'll make it into Ubuntu 11.10 as well.