If you turned off your computer and went outside, you'd save an untold amount of time staring at a casting bar. Just thought I'd throw that statistic out there.
Just some basic math regarding the mount casting speed change:
One hour = 3600 seconds; we're saving 1.5 seconds per mount, 3600 / 1.5 = 2400 mount casts for one hour of saved time.
If you only logged in to do your 25 dailies, and it took one mount per daily, after 96 days you'd have saved an hour of staring at a cast bar.
If all I was mounting for was herbing: assuming 3 herbs per node, I would get roughly 7200 herbs from those 2400 mounts or 360 stacks. Assuming it takes 60 seconds to locate and pick a node (I'd be surprised if it takes you that long, but who knows, maybe my server has a lack of herbalists), that extra hour is 60 more picks x 3 herbs per = 180 = an extra 9 stacks of herbs.