So, funny story: my todo list has this item, which I'm crossing off
with this mail:

compare f21 / f22 / f23 boot on rust:
https://blogs.gnome.org/mcatanzaro/2016/01/31/on-boot-times/#comment-120

It's only been on my list since 2016-02-06, no big deal, right?
However, never let it be said that I'm a liar! I *did* finally get
around to doing it, plus I included F24, F25 and the current F26
nightly compose as well.

I tested each by installing from the x86_64 Workstation live image to
my test box, which has a low-end AMD CPU (A4-7300), 8GB of RAM, and a
Seagate 500GB SATA hard disk (not an SSD). I created a user during the
install (so first boot wouldn't hit gnome-initial-setup before gdm),
then measured the boot time from hitting 'enter' on the bootloader
screen to GDM appearing fully loaded. I then measured the time it took
from hitting 'enter' on the password prompt to GNOME appearing fully
loaded. Then I rebooted and did the same measurements again (to see if
second boot differed significantly from first boot). I did not use
encryption.

The results were in contrast to mcatanzaro's from that blog post. I
found no significant difference in boot times across F21-F25. With only
one exception, pretty much every 'boot to GDM' measurement came out at
30 seconds, give or take a second or two, and every 'GDM to GNOME'
measurement came out in the range of 6 to 8 seconds.

The exception was the first boot of Fedora 21, which took a little over
a minute. The second boot took 29 seconds, though, in line with all
other tests.

However, F26 does seem slightly slower than F21-F25. First boot to GDM
for today's F26 nightly measured at 42 seconds. Second and third boot
measured 39 seconds. GNOME load time was 8-9 seconds. Looking at the
systemd-analyze info, I don't see any obvious single 'culprit', it
seems more like approximately the same stuff is happening during boot,
it's just all taking a bit longer.

So I'm *still* not sure what's behind the very slow F23 boot Michael
reported, but my test couldn't reproduce that slowness or show any
significant difference between any of the releases from F21 to F25. The
difference between F25 and F26 might be worth some independent re-
testing and deeper analysis.