Sno-Seal was the only boot treatment worth squat when I began to hike and climb. I fondly recall driving to Mount Baker many years ago in my robin's-egg-blue Karmann Ghia (now there was a car!), while my friend Norman tried to get enough heat out of the registers to apply some Sno-Seal. The boots had to be warm to apply it, see, and the little Ghia's heat vents just weren't up to the task.
In the past decade, though, new treatments have come outprimarily those that use aqueous wax or silicon. These have the advantage of being a little easier to apply than Sno-Seal, and perhaps a bit more compatible with modern silicon-tanning methods. They also are slightly more breathableSno-Seal was so effective that it tended to make the boots airtight as well as watertight, which could lead to sweatier feet, although I never found that to be a real problem.
But the bottom line is that Sno-Seal remains an excellent waterproofing treatment for boots. REI, among other stores, still carries it for $4.50 a can. I'm confident it's the only product to appear in both the 1943 and the 2003 REI catalogs.
Sno-Seal available from REI here.