Google is trying to link together their various services (Picasa, BlogSpot/Blogger, Plus, etc.). It's sort of a Good Idea™, but it's "not quite there," yet.
I'm one of those people who uses online services like Picasa as a cloud-based backup of my home storage. I use BackBlaze for my general data (really sweet service: I recommend it to anyone that has a good up-stream connection and gives a crap about protecting important electronic documents, images, etc. against hard drive failures or home disasters) and I (currently) use Picasa for my photo memories (Flickr has better storage pricing, but, when I was making the decision, Picasa had the better management software).
When I first opened my Picasa account, it was very much a stand-alone service. This was reflective of it being one of Google's many acquired services. Eventually, I noticed that images I'd posted via my BlogSpot account were automagically showing up in my Picasa account.
When I cashed in my Plus beta invite, one of the things I had to do was link my Picasa account to my Plus profile (no choice was given: if I wanted to try out Plus, I either clicked on the "accept" button or I couldn't do Plus - in retrospect, the latter might have been the better option). It didn't seem like too big of a deal at the time, so, I clicked "yes". I didn't post my first photo to Plus for several days after joining up (might have even been a couple weeks). It was several days, after that, that I noticed Plus-posted photos were showing up in my Picasa account.
Honestly, I think what alerted me to that fact was that Donna and I were out and wanted me to show some pix of our dogs to friends. So, I fired up my Android phone's "Gallery" application and noticed there were photos showing up that were from Plus. When I got home, I logged into Picasa and, sure enough, there was an album (tree) of my Plus-originated photos.
Sidenote to Google: data aggregation is great, in theory, but the way you're doing it for me - and not giving me any good method to manage or override - makes my data utterly chaotic: not good. At least give me options to determine what things appear in multiple applications. The first time I end up embarrased by your "helpful" stream-crossing, you can expect a subpoena.
It was mostly a shrug-worthy moment. I mean, at least I knew how to get at photos after I'd posted them via Plus. It did raise the concern of, "do Plus photos count against the Picasa quota I bought"? I'm hoping that what I discovered today indicates that the Plus folder-tree doesn't count against that quota: 1) it's the only album that seems to allow sub-albums; 2) unlike all of my Picasa-originated albums' photos, the Plus originated photos don't seem to be online-editable the way my Picasa-originated ones are. Dunno. It might be buried in a Google FAQ (or similar document) somewhere, but there's no quick indication of it.
I'll give Google kudos for making data available. Unfortunately, what Google really doesn't seem to get is that masses of data suck if you don't have good tools for logically-ordering them. And, no, I don't consider having a search engine to plow through the data-heap to be a good organizational method or solution for masses of data.