Just had a bad experience with the google+ Instant Upload album. Instant Upload is wonderful but the album is extremely unstable. When the album is filled up with many photos uploaded instantly from your mobile phone, it will break into two albums. One album contains the bulk of the photos and that album is immediately re-titled "Instant Upload xxxx - yyyy" (xxxx being the date of the earliest photo taken in that album and yyyy being the date of the most recent photo taken). A few of the latest photos remain in the new "Instant Upload" album.
When the break took place today, the bulk photo album just vanished. So what I now have is an older album called "Instant Upload 2012-02-20 - 2012-03-06" and the new album simply called "Instant Upload" but it only contains pics taken today. All my photos uploaded in the Instant Upload album from 6 March to today have vanished.
If you are using the Instant Upload album as the only storage for your photos, remember it's unstable.