ripplelabs updated their page concerning the xrp-distribution (https://www.ripplelabs.com/xrp-distribution/)
the available supply as of April, 30th 2014 is
7,817,888,647

not a huge change, but anyway you might consider to adjust the value accordingly.

Tried to buy XRP for BTC via Ripple client, without success. Anybody experience with it?

I granted sufficient trust to bitstamp's ripple address for BTC, USD and EUR.
I even managed to place an order the other way round (buy BTC for XRP).

However, when I want to sell BTC, the order won't be placed. It indicates
What am I missing?

Good question! I'd like to know, too.
Furthermore I just realized, I've been reading for at least half an hour now without beeing logged in 
Maybe this is the proof I'm really a newbee 

Yes, I agree, it is a big issue.
However, the idea behind it seems quite innovative and convincing.
In that point it differs from many alt-coins that are mere clones.

do you consider ripple an alt coin?
I do so for XRP (ripples), but I don't for the ripple protocol. And in combination I regard it worth beeing investigated further. To me it has potential as an alt-coin (in co-existence with BTC), alt-mtgox, alt-paypal and maybe more.
What do you think?