Altitude really does make a difference...

I just moved from sea level to 3900 feet, and I feel like I'm about to drap over cork-legged every time I run!

hmmmmm, i never thought about that.  I am training around 3000 ft elevation and I set PR in all three sports during my sprint tri in san diego (elevation 0) .... Now it is making a little more sense.

Altitude rocks! I live at 7,000 ft in Arizona and feel like I can run forever going down the sea level. People hate racing here because they can't breath, but I'm so used to it I don't know any better. =)

Oy, I remember that feeling. Moving to Colorado from San Diego was brutal. Within 24 hours of arriving, I was playing in a rugby tournament in Aspen (~8000 ft). I still remember the pain in my lungs, and that was when I was in great shape. It felt like they were on fire, and not just when I ran, but also when walking up to the condo at the top of a very slight hill. Ouch!

It gets better. And then you're super speedy at lower altitudes. I don't know if it's worth it, though. The initial adjustment was so painful.

I live at 4500 and can tell a real difference too. Generally a difference of ~2000 ft either way and I can feel it. It's great racing at lower altitude, rough racing at higher (Flagstaff...). But not as rough as for those coming from Phoenix

This is exactly what olympians at the OTC in Co Springs do.

Co Springs is around 6500-7000 feet. They do oxygen supplemented workouts so that they can raise the intensity of hte workout above what is possible without the supplemental O2. This is what is referred to when you hear "sleep high, train low"