2) Yes, that's why agreements with the MPEGLA are actually with the member companies (as mentioned in [1])
3) That was Nokia asserting against HTC three times. The first one was dismissed, the second one was rejected[2]. I'm having trouble finding any information about the third (which is at the ITC, not in a court), so it may still be ongoing.
[1] http://www.mpegla.com/Lists/MPEG%20LA%20News%20List/Attachme...
[2] http://www.osnews.com/story/27245/VP8_does_not_infringe_on_N...
1) According to that link the VP8 patents are licensed for use in VP9 (which I had forgotten or didn't know) but there is still the possibility of new patent from existing licensees in addition to additional patent holders coming forwards.
3) The reference you give is to one of the patents but there are more than one involved. As far as I know it is still an ongoing open issue.
Thomson created what is essentially an MP3 license pool, and yet, Sisvel cleaned out Cebit (one of the larger electronics fairs) booths every year (with the help of German customs) because some asian vendors showed unlicensed MP3 players.
It's still possible that some non-MPEGLA party stumbles over a patent that covers some tiny aspect of h.264.
VP8 has not been widely deployed (at least in hardware) to anything like the same extent so the possibility of lurkers is greater.
Getting products pulled from Cebit (and German Customs helping) is for me a completely wrong on so many levels I can barely describe (at least if the products weren't for sale to the public).
2) MPEG LA doesn't have patents they invite patent owners to contribute them to patent pools for a cut of revenue. Where companies have not been involved with the development of standards they are not obliged to license them on FRAND basis so there is more reason not to join a pool. Nokia at least is in the pool for various MPEG standards but not VP8, there may be others waiting to troll if large scale use occurs.
3) Nokia hadn't joined the VP8 pool and was actually using a VP8 relevant patent against an Android manufacturer. I don't know the current status of this case but if you have a link to recent news I would be grateful.