Trip to the amusement park.
With the near ubiquity of web access through my iPhone, when I look
at a serious productivity app, a high-priority requirement is to have
useable access from both laptop/desktop and iPhone. If offered only
through a browser, rarely can the one interface work on both devices
well. Even simple navigation events like a double-click or scrolling
are problematic on an iPhone, not to mention the lack of Flash.
web app developers that want wide acceptance need to either introduce an installable client for the
iPhone and a decent API, or provide an iPhone-friendly web interface that can
be accessed safely over Safari. For some apps, only one mode of access
makes sense (GPS-related mapping for example), but for others it's a
major turn-off. This isn't just limited to iPhone of course: Android and (soon) Palm Pre users will have the same requirements. And it's not going to go away. Increasingly, more users will be accessing apps through a smartphone than a laptop. If nothing else, any web app should have a good public API and let the market come to the party with different ways of accessing and manipulating the content.