Widgets can be installed or open. Only open ones use resources (aside from disk space). Open widgets only use CPU when the Dashboard is open but they do each consume 5-10MB real memory and about 220MB virtual memory (most of which are shared libraries) all the time. There's only one screens worth of widgets, they can overlap but that seems less useful, so screen real estate is valuable. Therefore I want to be somewhat selective in the widgets I use.
There are a lot of third party widgets available from or Apple or Dashboard Widgets but I find only a few things work well as widgets. Widgets that wrap search engines or RSS newsfeeds are better done with browsers (Safari) or newreaders (Vienna). I use the OSX dock and often the icons show status like new mail, so I don't need email or IM status widgets.
In spite of the above limitations there is a set of things I've found very useful as a widget. Something that I use frequently enough that I want it easily available though not so much that I want it on the desktop, and that provides information visually (for some reason widgets should be pretty). Below are the widgets I have open all the time. First the Apple supplied ones.
- Weather - I probably check the weather 3 times a day and this widget remembers where I am, shows a lot of info, in a little space, and is very pretty.
- Dictionary - In modern (aka Cocoa) apps you can highlight a word and type Command-Control-D to get a popup dictionary definition. It's great, but not all apps are Cocoa. Quicksilver has a Lookup in Dictionary function, but sending a word to Dictionary.app only works if the dictionary is already running. So, copying a word, bringing up Dashboard and pasting it into this widget works pretty well.
- Calendar - Nice to see a calendar in easy reach without having to open iCal. Since the clock in the menubar doesn't show the date, this is an easy solution
- Stocks - Just like the weather, it's easy to check several stocks a few times a day
And the third party ones:
- SysStat nano - This is the best of the system status widgets. It's very small and the overview shows CPU, Memory, and Disk Usage, network throughput, and temperature.
- AirPort Rader - This isn't planes but Wi-Fi, shows the strength and channel of available networks. Nice to see the channels so you can set yours to be a different one
- RadarInMotion - This is a great addition to the Weather widget. I have it cycle between a radar and satellite view. It uses a lot of memory but it lets me know if that 30% chance of rain will actually happen where I am.
- iCal Events - The Calendar widget should show your upcoming appointments but it doesn't so this one does
- YOLK Mini - I use this for 30 and 60 minute times for laundry.
- StatCounter - I use to monitor hits on this blog.
- Say Cheese - This shows several daily comics. I use it to read Calvin and Hobbes reprints. it minimizes to a nice small voice ballon.
- RPN Calc - If you don't konw what RPN is, skip this. If you do, this is my favorite. It doesn't waste space with number keys assuming you'll use the keyboard for those anyway.
The following widgets I use infrequently so I don't keep them open all the time:
- Widget Updater - This widget checks your installed widgets on various sites to see if there have been newer versions posted and will let you download them. Easy and great.
- Sudoku - generates a random puzzle and lets you solve it. Allows you to make notes in each square so you work just like paper and pencil.
- Sing that iTune - will lookup the lyrics fo the currently playing song and display them. Can also copy them into the notes portion of audio file.
- DashTunes - Tiger ships with an iTunes widget that lets you play, pause, skip, etc. But it doesn't let you rate the song, this widget does.
- Translation - Every once in a while I'll want to translate some phrase into english, this does fine.
- Unit Converter - For the ocassional convertions this is most convenient.
- Package Tracker - When I order something online I want it now. Rather than look the email with the link to the order to find the link to the package tracker, I enter an UPS, FedEx or DHL number in the widget and it displays the current location of my delivery, easy to check obsessively three times a day.
- Easy Envelopes - A cute widget that looks like an envelop, lets you search through your address book for a person and will print an envelope addressed to them. Since it remembers the print options, it's faster than using the Address Book directly.