Hi,
I just got my Vaja Billfold Flip case yesterday and love it. Though I mistakenly ordered the billfold portion... they do make a non-billfold version as well.
Pros:
1. Flip case - not like the proporta's aluminun cases.
2. Billfold section has a clasp to keep it secured until I need to open it. I can flip open my case and keep my credit cards and bills safe.
3. Flip cover has a clasp -- I think the proporta flip case has a magnet system
4. easy access to headphone jack (optional), CF and SD slots (optional), and sync connector
5. speaker is covered by a mesh screen to protect it, yet keep the iPaq audible
6. Feels secure in the case
7. Good quality
8. I've managaed to combine my wallet and my iPAQ into 1 component!
Cons:
1. getting to the stylus is a minor inconvenience
2. "push through" power button is not so "push through" -- I have to try a couple of different angles. The power switch location on the case is not exposed -- they have some knobby thingy that allows you to supposedly push-through the case to hit the button.
3. no slot for CF card storage... I have a CF WiFi card that I have to carry around in my backpack now...

If I insert my WiFi card, now I have to carefully keep track of my CF slot cover...