Tipping is hard - Marginal REVOLUTION

And should I also say that writing software is sometimes easy? Stephen Dubner lists some of the new iPhone applications:

iTip, from palaware
iTip, from Uncouth Software
BigTipper, from PureBlend Software
TipCalc, from BAMsoft
Tiptap, from Made with Bananas
Tipulator, from tap tap tap
Tip Calc, from Charles Ying
Tip, from Carlos Perez
CheckPlease, from Catamount Software
Tips, from Kudit.com
mTip, from Pascal Mermoz
TipBuddy, from Justin Jeffress
Gratuity, from TapeShow
QuickTip, from Spare Change Software
Tippety Split, from Manta Ray Software