I've experimented, and I'm sharing my results! OK here's what I have and what I've tried:
I got the Avery stretchy transfers for light shirts at
WalMart, and I used one on a pillow case (I know it's not stretchy, but it was a test!) and the other on a 50/50 shirt from Michael's. It worked well -- it did stretch like it said it would without showing cracks. The black on the mouse ears on my design didn't all transfer to the shirt though -- it's got some white "dots" on it, but it's not too bad.
Any ideas on that?? Do I need to iron longer?? Here, you can look -- see the left ear and through the middle of the head? Isn't that weird?
Avery does not seem to make stretchy transfers for dark shirts... yet. From a hint on this thread, I found some at Michael's. They are "Tailor Soft 'n' Stretchy." While they also stretched without ruining the design right after I ironed them on, they appear to all have a shiney one inch in width strip down the middle of the page (you can see it on my design on the shirt below)!

It didn't go away with ironing like I hoped. Not sure what that is, but I'm just going to ignore it... it's a homemade shirt, it's not perfect.
Anyone ever seen that on transfer paper though? Any ideas? I do mostly like the results though. Now that I've done the shirt shown below, I'm cutting closer to the design going on a black shirt since the black ink obviously doesn't match too well... There does look to be a small crack in the bottom middle on this picture, but it's not really visible IRL.

This is also a Michael's 50/50 shirt.
Since my shirts tend to stretch a bit across the top no matter what, I'm going to stick with the stretchy transfers. They look "good enough for government work", as my dear Grandma used to say.

I'm not going to DW until Jan 09, but I want to get my shirts done before the school year starts and I'm off teaching again, so in a few days I'll have all my shirts done and stored away waiting for our trip!

Oh yeah, I've opted out of washing them (in vinegar or otherwise) before the trip. I just want them to look great on the first wear at least!
