Once more, with feeling and four-part harmony....
1. Tools that operate on pixel opacity instead of RGB. Many times I wish to clean stray pixels in a layer, and the workarounds are annoying. I want to select by opacity (with all the selection tools), and be able to manipulate a layer's opacity info with a Levels-like tool. Doing things with interim alpha channels is very time-consuming and introduces many opportunities for error.
2. Save As option to recall the last Saved As folder and format, for each open file that was Saved As during the current session. I keep source PSDs in one folder tree, and output TGAs in another. And Save As, every time, takes me to the folder the PSD lives in. I don't mind that the first time, but every time, that makes for a lot of renavigating the folder tree in the dialogue. The Recent Files link is ineffective, because I have destination folders that share a naming convention (so there are lots of "sourceimages" folders, with no context as to which is which), and because I see often that certain recent files just don't make it into the list, for one reason or another. I continue to pray for this.
3. When saving a PSD to an alpha-supporting format, a dialogue to choose which alpha channel I wish to use. Right now, if you have more than one alpha channel, you get none of them, but instead get a pure opaque alpha channel.
4. When you Save As to an alpha-supporting format, please look at the image and make an assumption about 24- or 32-bits based on the image. Current behavior is to use whatever the setting was the last time you Saved As to that format. If there is no alpha channel present, assume 24-bit and default the dialogue to that. If there is an alpha channel present, assume 32-bit and default the dialogue to that (and offer me a list as to which alpha to use, per request #3). I often embiggen images that could be 3-bytes per pixel and are now 4, or I blow away the much-desired alpha channel, because the dialogue uses whatever the last setting was.
5. I'd like a more interactive Offset filter, similar to the arbitrary canvas rotation that we have now (yay to that, of course). I offset the image within the canvas window, work on it, and hit Esc to have the image invert the Offset. This would make doing tileable textures much easier.
6. Also in-line with doing tileable textures, I'd like layer styles to act as if edge pixels repeat infinitely off the edge of the canvas. If you have a horizontal line in your image that has a drop shadow, the drop shadow shows artifacts of the lack of extension of your layer data off the canvas. The workaround is to put off-canvas info there by sliding the layer over, painting in some pixels, and then sliding it back. But this then screws up things like your ability to Offset that layer if you need to. A general behavior like I describe would make life much easier if you use layer styles in images intended to tile.
7. Temporary brush palette. Many times, I hack together a quick brush for one tool, and would like to apply it to another tool without the hassle of creating a preset. If there were a "six last manipulated brushes" palette (that did not include size change as one of the changed parameters), then I could easily apply one temp brush to another tool.
8. Global brush size option, and lack of required size specification in brush presets. Brush size is something I change all the time, and is not something I really care about when saving a preset. And when I'm working on something, and flip back and forth between, say, eraser and brush, I'm generally working at one specific scale. I'd like an option to have all brush-style tools (stamp, brush, pencil, etc) all just use one size value, whatever the current size value is. When that option is set, the size specification in brush presets would be ignored.
9. Editable presets. Right now, you have to load the preset, change some aspect of it, save a new preset, and delete the old one. Let me just resave the existing one. Like the old days.
10. A new one! I'd like Image Size and Canvas Size to not automatically use my default unit type (which is pixels). I most often do percent adjustments with those panels. If there could be a preference for those panels that would stick, session to session, that would be nice. I don't know if that's too picky: I just find, especially with Canvas Size, that I'm always changing that value to percent. I haven't found any issue with any other feature using my global choice of units, just those two. I have no idea if anyone else finds themselves working this way.