Judging by what many people have said, mainly and mostly Arch linux users, have to conclude it is faster and parallelizing bootup, one of the advantages claimed. However ... brings me to the next point/question. Which version was used here ? The one in testing and unstable is like 3.15, don't quote me on this, think last time checked the one in experimental was 3.18 and in Arch it's no doubt or almost no doubt, whatever is the lastest version of systemd.
Think common sense dictates that bugs were found and squashed and/or features added between 3.15 and .18 ? Again that would just be a reasonable assumption imo. When a newer version is released, makes sense something would be different and hopefully better in it.
One of Arch linux's trademark, the whole our distro is cutting edge latest thing. Back when did try Arch, yeah I liked it and had no problem admitting it can be great, though readily admit Debian is great imo/experience too. Had a minimal Sid install and an Arch install side-by-side and from what I saw 1st hand, sometimes I'd check the unstable repos and compare what was avail in the Arch community repos. Sometimes the versions avail would be the same, sometimes Arch would have newer, sometimes Debian would.
(Edit: nope self-correction on the above, had the Deb experimental repo enabled in that case, am almost sure anyway and don't/didn't like the idea of using it often.)
Also both have additional repo's someone who wants to can enable, Arch has a few, one option being the AUR and really Debian does already have an equiv to it. That being Debian-based Sid distro's, who are 100% Debian compatible that maintain and patch software that may not be avail in Debs software repos, shrugs. For me personally in Arch the community repo was good enough and in Deb/Sid, didn't really want to mess w experimental often either.
Not to mention the tons of other ways someone can get access to newer or even exotic packages not readily avail in a Deb repo. Just saying, judging by the feedback of quite a few Arch users, too many keep harping about a very noticeable boot time improvement for me to believe they're all fulla-chit, more shrugs.
Another thing that occurs to me, there are several other outside factors that could improve or degrade init whether someone is talking about sysv or systemd( for that matter OS function overall PERIOD, including all sys resources o course), not going to bother listing all of the chit-ton of them. If ya don't know, then ya don't, google, experiment and learn all the ways to tweak and enhance a gnu/Linux OS = any distro. With some know how a person can get an outdated system, booting faster than a much higher spec system that's in the hands of an incompetent user. Within reason of course, not talking about an SSD w a dual-quad core vs a 512mb ddr2 w a P4 cpu.
For me though, definitely have more important things to do, than sit in front of a pc w a stop watch anyway. By this pt ... couldn't care less what init system anonymous nixers prefer, for whichever reasons.
Jessie hasn't even gone stable, so which version of systemd it'll come w default isn't set in stone. Nor is the gazillion other easy options people have availabe to them, to use something else. For sure 100% it's all about choice, application and skillset. Have absolutely nothing against people using whatever they prefer.
Edit2: Oops cr&p, another thanks to the OP, is interesting and to other community members who shared opinions/insights too.