I meant to reply to this - this is a really good and important point, and I think a good place to move the discussion.
You're right, most people will never get their Vo2Max tested. Fortunately, this isn't necessary. In training, we aren't so concerned with the actual, stating value of an individual's Vo2Max itself. Even with elite athletes, we don't test Vo2Max for the sake of getting the Vo2Max. This is all done to determine race pace at Vo2Max, and time to exhaustion at Vo2Max.
What the amateur running community has been doing with success:
-One, recognize that Vo2Max is linearily correlated to HR (and will be between 88-95% of HRMax for most people).
-Recognize that an individual can perform work at Vo2Max for between 5 to 8 minutes (the point at which you reach Vo2Max will of course differ based on fitness levels).
So, we know that your Vo2Max will be essentially your maximal pace for 5 to 8 minutes. It's an unfortunately long gap, acknowledged. But it's a starting point, short of getting tested.
So we have you do a 5 minute time trial to approximate your Vo2Max pace (a 12-13 minute time trial would probably be more useful, since that gets you closer to 95% of Vo2max, but when dealing with amateurs this is too subject to variability from blood lactate, biomechanical efficiency and willpower). So we set Vo2Max zones based on this 5 minute time trial, keeping into account your HRMax and what percentage of HRMax this is. Then, we adjust as appropriate. If you are consistently failing the intervals despite being fit, your Vo2Max setting is probably set too high. If you are consistently breezing through your intervals, your Vo2Max setting is probably set too low. This is the trial and error portion, and it will take a few months for you to get your setting dialed-in. (Some people just recommend skipping the time trial and multypying HRmax by .9-.95, but I think this is flawed because it also assumes you have an accurate HRMax figure, adding additional variability to an already variable determination).
The time trial is not perfect. It has flaws, since it's not 100% precise. But you can gain some comfort to mitigate these concerns, by the fact that we are merely targetting 95% of Vo2Max for most of our intervals. It's OK to be off by a few percentages, as long as you don't get too close to 90%, and you don't get too close to 100%. (word of caution: reying on perceived exertion is very inaccurate because this takes into account muscular fatigue and blood lactate levels, which have nothing to do with maximal aerobic power.)
If you don't think the above is worth it, this is fine. Intervals and Vo2max work isn't for everyone. Personally I haven't done proper intervals in years. Not worth it for my goals in cycling. A cycling race may help you, although I think this works you at LT intensities far more than Vo2max, and thus comes at greater cost.
I do think working on Vo2Max is important even for amateurs. This is because 95% of maximal aerobic power is 10-14 minutes of exertion, which coincides perfectly with many climbs, time trials and breakways, not to mention other shorter riding scenarios. Work specific to the task at hand, and all that jazz.
Whatever you decide, we really need to understand our goals and the rationale (and flaws) for the various options to achieve those goals.