Pfew... some more misinfo!
I think everyone knows that R134A is one of the most handicapped of all popular refrigerants. (if anyone else didn't, now you know!).
As for R290, here's the MSDS for it, ya'll can judge for yourself:
R290 MSDS . In short, it's not so much using it that's a problem, it's storing and handling it. You should know how easy it is to have a refrigerant leak, especially in a home made/modded system.
I think it's clear that R290 is OTHERWISE a good choice.
Here's a link describing (to some extent) some popular refrigerants.
Here's a link for the DIYer.
Here's a fat PDF listing most refrigerants.
Here's a freeware one can download to calculate the pressure effect on some refrigerants.
Here's a review of the software (!).
You seemed to have missed ymboc's point: talking to ONE person isn't anywhere near enough of a good sample to make a judgement, and certainly not enough to make a generalization.
If spending 4 hours with an HVAC tech didn't get you anywhere, well, I'm sorry! Try somewhere else.
(For the record, I post at many other forums)
I'm going to go read a paper now... and see who else blew themselves up!