Acorn 3.1 was released a couple of days ago, and one of its new features is support for 10.7's autosave and versions. The early betas of Acorn 3.1 had this turned on by default- but in the end I turned it into a preference and set it to off by default.
Why? Turns out more people hate 10.7 autosave than like it.
Before Acorn 3.1 shipped I had a little inkling that maybe folks weren't too happy with it, so I reached out for opinions and I only got negative responses (I did however get my first positive reaction after it shipped).
I think I understand the scorn for it. For one, it can take a perfectly good image and ruin it! Allow me to explain:
Someone sends you Photoshop document with meticulously crafted layers and you open it up in Preview on 10.7 to check it out. Preview can read a PSD file because Photoshop will write a special hidden layer which is a composite of all the layers put together. You only get to see a single layer in Preview- but it's exactly what Photoshop shows, and that is good enough for most folks. Preview can also save a file as a PSD- but it will only save out the single composited layer that it originally read in. All the other layers will be thrown out.
Do you see where I'm going with this?
You open up the PSD in Preview, make a minor edit to it such as adding a little text to it or draw a couple of red lines. The intention is to select all, copy, and go to your email app to paste it into a message. You'll just undo the changes or close it without saving later on.
In the background, when you left Preview it autosaved the file and destroyed all the layers. You even quit Preview without thinking, so you didn't get a chance to decline saving it.
Now, you could then reopen the image in Preview and use the "Revert Document…" menu or you could use Time Machine to get an older version back, but wow that's annoying.
I'm not saying autosave is bad. I personally like it (most of the time), but that's because I edit any images I care about in Acorn's native file format. But if you usually open and edit PNG or JPEG files with autosave turned on, then you're going to be in a bit a hard spot eventually.
I think long term apps will probably only allow saving for file formats that that can restore the state of the document exactly as shown. You can already see this being done in apps like Pages (4.1)- you can open up a Word document, Pages will create a new untitled document based off of it. You can only save a copy of it as a Word doc. Maybe TextEdit shouldn't be autosaving word documents? And maybe Acorn will eventually follow Page's model as well.
I think this kind of a change might be too big to put in a minor update, and I'm not really sure the majority of folks are ready for this type of change either. But it's something to think about.
Of course, Apple did add autosave support to Pages in version 4.1, so that's something to think about as well.