I have been recently using the iXpenseIt iPhone app to track cash expenditures. What's interesting is it uses the "most used" / "most visited" feature (which you may be familiar with in Firefox or other software) to vastly speed up its usage for the individual using it.
Let's take an example, this is my default "New Expense" screen:
Notice the entries - default vendor is "Shop", default category is "Household" and default subcategory is "Supplies." (my preferences).
Let's say I had gone out for a Saturday afternoon lunch and I want to quickly enter the food bill. I type 'Re' and it quickly shows the best auto-complete option from the list of vendors:
When I tap the 'Restaurant' pop-over, a small neat thing happens - it shows me the frequent categories I used for this particular vendor:
So I tap on the second option and voila, the correct category and subcategory is chosen. The funny thing is that this simple "most frequently used" gimmick is the sole reason that I'm still using this expense tracking app (after all these days of trying so many of them) because my time to add a new entry goes down 3-5x times over time!
Another example - consider my favorite note taking application Evernote - when I go to the 'Add New Note' option and the clock happens to be in the middle of a calendar event, the default title of the new note will be "Note from Event Name":Why is this useful? Because that is the most likely thing I'll be doing - adding a note from the event that I'm attending, and this speeds up the process of me writing the new note. I wish more applications would do this, for example:
- I'm currently in Pune where Airtel does not have a 3G circle permission, so I am told to switch to Idea network or Vodafone network to get 3G access, but the hitch is that there are areas where Idea network signal strength is low and I have to manually change the network back to Airtel which has full signal strength. I really wish my smartphone could remember which network I use in each of my frequented locations and automatically switch based on that.
- I wish my Email application would show frequently emailed contacts when I click on "Mail this link" in my browser. Apple has a new VIP feature in Mountain Lion but I just wish it could show my "top 5 most emailed contacts in the past month" immediately next to the "To" entry field that I could just click on! (I couldn't figure out how to use the built-in Mac OS X Automator software to simulate this)
 I don't intend to use it for more than a few months, it's just to get a handle on expenses when living in a new city.