nagromme said:
1. TV schedules!!!!!
2. Movies!!!!!
A QuickTime widget exists already--if it's not included, check out dashboarddev.com (now dashboardwidgets.com)
Also already made.
5. Unified "new email" status for your OS X Mail AND free accounts like GMail... AND FAXES all in one. A clickable icon and number for each service.
Mail checker widgets already exist, and one of the major points is that you can have multiple instances open. One for every account, as it were.
7. Shrunken "big thumbnail" view of any Web page(s) you want to watch, refreshing at any rate you choose, with an icon to indicate a change, and another to indicate the site is down.
Plenty of minibrowser widgets around.
9. Mini iPhoto browser: pick album from a popup, cycle photos with arrow buttons. Click to launch iPhoto and see photo at full size.
I could have sworn I've seen something like this somewhere, but now I can't find it.
10. Draggable magnifying lens that looked THROUGH the black background and enlarged what was underneath, say, 4x. I'm guessing that the underlying image is accessible to Cocoa developers in some way, so a portion of it would be enlarged and rendered in the widget. Preferably updating live.
This seems like something that shouldn't be a widget at all, but an applet that runs outside of the dashboard for normal use. The dashboard isn't meant to interact with the desktop workspace directly in this manner.
This was a great list of practical and useful widgets! Thankfully, most of your wishes have already been met. I highly recommend
http://www.dashboardwidgets.com as it has several really useful widgets (and a healthy number of utterly useless ones, but your mileage may vary

).
As for the original post's idea, I don't like it. The idea is good, I mean it's a really great mini-GarageBand interface that would be really helpful, but as a widget it would be unnervingly complex and unwieldy. Widgets luckily aren't constrained to web-centric languages, so it would be possible to write a mini-GB, but with tremendous system resource useage and a fairly complex interface. It would also need to call a huge number of GB functions to the point where GB would essentially have to be running, and at that point, you might as well just use GarageBand. Frankly, I'm glad I don't get paid to do Mac development of any sort at my job--because now with Tiger, I'd be asked to create immense widgets to handle all sorts of tasks that need full-powered applications. They'd be asking for Dreamweaver: the widget from scratch with all features available.
I'm fiddling with a few widgets for some database entry and manipulation though, because I get to do graphics and artwork and not too much boring programming (despite being a sysadmin, I hate programming! I'm an artist by nature). I see this as the greatest business potential for Dashboard: custom-built widgets for those repetitive data entry/recordkeeping/report-making tasks that can always be available without being in the way. No more need for 7 browser windows and 3 bulky applications sitting on your desktop. With the pages already written, I just have to make a modified copy to pass the right strings and variables in the widget with a minimum of PHP/SQL dirtywork. Need to make an entry in a database? No need to navigate to the right server, log in, and find the correct entry page anymore. Just hit F12 and start plugging away. It's a thing of beauty.