What compels you to  use an application? There's a number of potential features, however, there's several things that will almost always convince me that I need to give an application a try.

Location - This is a no brainer, but perhaps the most compelling feature that an application can provide me along with the experience is location provisioning. Given that pretty much everything has a location component (physical location, a particular place that is sensitive or important to a certain moment, etc…) grabbing and using a location fix is key… it also enables the ability to produce useful spin-off products like a GeoRSS feed! Real map integration, not simply kicking me out to Google maps is a great feature as well!

Mobile Support - just about every one of my favorite tools also has mobile support… and hopefully not simply basic web access via a mobile web browser but a full-blown mobile application. I look at apps like Qik, Traffic.com INRIX traffic, Flickr, Twitter, facebook, Brightkite, Dopplr, Google Maps, Nokia (Ovi) Maps and many others of fine examples of this. If at all possible, integrate the ability to capture and share photos and video with the service as well… I’m currently using some fine mobile apps on my iPhone that could be ranked as “excellent” if they would have included this functionality.

Social Media Integration - if I’m using an application for any reason I’m pretty much always creating content of some kind, sharing information, or doing some kind of search and discovery… having the ability to share the results with colleagues, friends, even myself via my social bookmarks is crucial. Every app (social, personal, or enterprise use) needs to provide me with the ability to connect to some of my frequently used tools like the blog, Twitter, facebook, even dumping content to an RSS feed would go a long way.

Price Point - Free is always nice but that doesn’t mean that I’m not going to pay for something.. heck, some of the coolest apps I’m using (Mobile, web, and PC) are free tools, however, many of them I would be glad to pay for… too bad the developer didn’t know that! Before you roll out your app think about using a group of Beta testers to get some feedback on the price point - sales channels are also crucial in this step as well. There’s some great apps out there that are over-priced, however, there’s also some fine free apps out there that could easily be generating some good revenue - think about adding enhanced features for a “pro” version though.

Support - If I’m thinking about buying a product (particularly an application or piece of software) I’m really jazzed by having the ability to connect with other users, real staffers, and product evangelists that are eager to share tips, tricks, support, and share examples of successes that customers/users have experienced. A good group of product evangelists will go a long way in selling your apps and services. I’ve gone on to use apps much more frequently mainly because I’ve connected with the developer team via social networks and received some great tips and help as well!