Sorry to hear you're having problems. I actually have an EVO 4G as well
myself, but no longer with cellular service. I've changed the ROM to run
Cyanogen Mod so that I could test out with a non-HTC ROM. I also have the
HTC Thunderbolt, which is very similar to the EVO in specs.
The issue with the white screen may be a result of viewing old videos. A
little while ago, Vimeo only encoded videos in Flash video format, however
now they encode in MP4. For older Flash encoded videos, instead of using a
video player, I use the built-in web browser and embed the Flash Video into
a page. This is the reason why you see a white screen.
As far as downloading/playing, I'll take a look into the issue and see if I
can reproduce and fix it.
Appreciate you taking the time to let me know about these issues. We just
moved into a new house a few weeks ago and between work, fixing up things in
the house, unpacking and watching my son, it's been leaving me with little
time to focus on improving the app lately.
-Makoto