I've been using the free meter app for my iPhone and while it won't replace my dedicated meters for specific applications (when I need 1-degree spot metering, or incident metering, or flash metering), since I always have my phone with me, it is very convenient for general walkaround shooting. I've found it to be very accurate - all of those recent shots in my gallery of the museums in DC and the DC Metro were metered with my iPhone. Would I use it for a paying gig where critical color rendition was required? No, but for my own purposes, out and about, it's more than good enough. The big downside to it is that it is a battery drain on your iPhone, so it is possible to 'lose' your meter when you need one if your iPhone conks out.