Since I put up that session (2 x 2 x 400 with 2 & 5 min walking recovery) I'd like to address a few of the comments.
Firrstly to 800 advice - this is a tough session. There is no way I would do it within 7 days of an important race. However, I WOULD do it 9-10 days before an important race as the last hard 800 session. You can recover from it in 3-4 days if you don't train too hard in between - I mean you can race an 800 3-4 days later if you want, but not your most important races.
Young master I think it's logically harder for 400/800 types because of their lower fitness levels. However, remember they have a bigger 400-800 differential (their 800 speed is further below their 400 speed) so running the 400s at 6-7 seconds off their 400 speed is easier than a 10km type running them 4-5 seconds off their 400 speed. It works both ways. A 10km trained runner will recover well between intervals and sets, but will really have to be pushing it. A 400/800 runner finds the 800 speed further below their faster speeds, but might struggle with the recoveries.
Also yes, I would treat it as a near peak workout. If you have a 6-week anaerobic phase, and you did a hard 800 session once a week, I'd approach it something like this:
Week 1 - 2 x 6 x 200s [30" walk and 5' jog]
Week 2 - 2-3 x 3 x 300s [1' jog/walk recovery down the straight back to the start, 5-6 mins between sets - useful if there's a wind as you recover into the wind and do good quality with it)
Week 3 - 2 x 2 x 400 [2' & 5']
week 4 - 3 x 500, 5-6 min rest
Take week 5 and 6 where you want (mix in 400/800 sessions or 800/mile sessions, mix up the reps and where on the track you do them) or need to, but I'd go back to that 2 x 2 x 400s as the last session before a bigger race.
I might add I find a session of diagonals every 2-3 weeks during base really useful. By diagonals I mean run the diagonal of a football/soccer field, jog the base line, run the diagonal, jog the sideline. You just keep turning right or left and it works. Do it at close to 800 speed, and try to get up to 20-30 of them (110-125m each). It gets that fast relaxed stride imprinted on your subconscious, and you can click into it as you start on faster work.