For me the worst part of the entire experience is driving up the steep, dirt/gravel winding and sometimes narrow road. If the washboard surface and hairpin turns are not enough to make one feel uncomfortable, then the racing 4-wheelers certainly are. The riders on these ATVs seem not to care one whit for safety, and I would expect that around every sharp corner there could be one or two of these things smack in the middle of the road. The canyon road is, in my opinion, made even more dangerous by the presence of ATVs. Allow at least 35-40 minutes to negotiate a one-way trip up or down the canyon itself.
The two gas stations on hwy 89 are not the same anymore - one is a sinclair (on the east side) and I believe it is a Tesoro (on the west side). From there it should be the same.
The exit to U.S. 89 from I-15 is now #324. There is no Exit #326.
There is an additional trail along the north ridge of Adams Canyon (http://www.summitpost.org/adams-canyon-north-ridge/164098)
Also if you happen to be headed up to Thurston, there's a notepad (log book) in a container near the marker. The notepad is almost full, so it would be cool if someone took a new one up there.