Interesting. I didn't know about this.

Tried it with following so far:

1. Midnight Commander - Perfect (but it doesn't remember next time)
2. Contacts - Great but not perfect fit.
3. Photo - Okay (photos all gets cramped up. it's actually not bad)
4. fmms - Doesn't reorient/fit well.
5. Conversations - Initial page is fine. but not in sms etc.

At the end, it's not that special or useful yet. Guess most apps were never created with portrait orientation in mind. Ah well. I'm fine with landscape.