Out of all the tools on dA to reward excellency, I do think the Daily Deviation award is one of the best and most satisfactory. But when someone builds onto that system, and makes it easier and faster than ever to suggest DDs, it eliminates the laziness that was probably holding back more than 80% of people who would normally have suggested a DD. (I know I'm one of those )

Suggestion Warnings
Amazingly useful feature, which probably both saves the GMs a lot of work and at the same time instructs deviants about the rules of suggesting.
If anything, I'd say have a couple more warnings to add to the variety. But really, this is perfect already.

GM list
Another great idea, which has often saved me the trouble of having to look through FAQ 18 constantly.
I like that it shows multiple GMs, just in case you have a preference or believe it belongs more to one category than another.
I also love that there is a space for one to type their own!
Nothing at all!

Tooltips
A very useful feature, as one might not know what a certain function does.
I would suggest going a tad bit more in-depth with the tooltips, notably the one entitled "Suggested Description." Although I know what it does, the tooltip might be a bit hard to understand for someone new to it all or whose first language is not English.

Suggestion Counter
A nice addition, albeit a little random, but I suppose some people might want to know how many they've suggested so far.
At first, I thought this counter was one that showed how many times the specific deviation had been suggested before you. I think that would be a good idea to have.

Preview Tab
A nice feature, which allows you to use the full screen SuggestDD while also seeing the deviation.
I noticed that when suggesting something small, such as an emote, it is drastically enlarged and looks really weird. Perhaps a good idea would be to specify the script as such: Make deviation previews be their normal size unless that is larger than the preview dimensions, in which case they would be sized down.

Anonymous Suggestion
Although I don't particularly see a point to this, I suppose it's a good thing to have if one wishes to remain humble.
Nothing!

Mini Mode
A great addition to have, as one might want to have less
The drag-and-drop feature is perfectly executed, and has proved itself extremely useful!
One thing I might suggest is to have an option that says "Always Show in Mini Mode", or "Always Show in Full Screen Mode". This would be useful if someone likes using SuggestDD in Mini Mode and doesn't want to constantly re-switch to mini mode every time.

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Overall
Great work on this feature! The whole thing works very smoothyl I can't wait to see more added on to this already great program.

What I would suggest is to change the note subject: I'd make the subject say "DD Suggestion" or something of the sort. As a Gallery Moderator, I would probably sort my notes based on which ones specify that they're DD Suggestions IN the topic, so that I wouldn't have to look at the note to double check.
Someone could very well send a GM a note with subject "Deviation by Username" but just have it saying how they enjoy it.

Nice work!