I don't want to destroy your plan, so have in mind that I am negative about Launchpad when you read this ;)
I have no "plan". ;-) I don't want to destroy any workflow of Arch. It's just an additional help for people who uses launchpad for meta-bugtracking.
First of all: why? Do you think anyone of the Ubuntu guys cares more if a bug is also marked as being valid on Arch?
Well, you shouldn't bash against Launchpad because it's from Canonical and they released Ubuntu. Most times people are against Ubuntu they are just envy of their fast success. ;-) Anyway... I don't want to talk about THAT. Ubuntu is nice but has some problems like every other distro... but Ubuntu != Launchpad. No one should report bugs to launchpad instead to Arch's flyspray (if that will happen, I will forward it to flyspray). But you can link some bug-reports of other distros (Gentoo, Fedora, Debian, ...) to a flyspray-bug in Arch. It's nice to have those meta-bugtrackers because you can see the progress in other distros and look for fixes. Another example: https://bugs.launchpad.net/gentoo/+bug/203997 You can see that Distro XY needs to fix that security issue. (Idea: if you link Arch to that, it could send an eMail to security-issue@archlinux.org)
I mean (and that's imho part of the arch philosophy), the best thing is to get bugs fixed upstream and not report them to "Ubuntu".
You won't report it to Ubuntu... most times it's already reported to upstream (or will be forwarded to them) in launchpad and you can link this to Arch.
Second: Launchpad features may be nice (and even superior to self-hosted stuff (eg. Trac)), but that only applies when you use most (read all) parts of it. (Including bzr for example).
Of course... but meta-tracking bugs is a nice feature. Even if you don't use anything other from LP. I don't want to persuade you to use LP. If you don't want to use it, you don't need it. ;-) But maybe you will like some preferences of LP you don't know. ;-) Regards, André Klitzing