The potential uses of MIDs are just as varied as the hardware choices. They can all be used to access the Internet. But their capabilities depend heavily upon the hardware components they contain and the OS version they are running, which affect whether or not the available apps that you can download will actually work (or, in the case of your device's flash memory, how much will actually fit on the device). Some MIDs come with manufacturer skins installed over the OS, with a certain set of preinstalled apps and perhaps more available for download from the company. But most have access to one of the previously mentioned app markets, allowing you to choose how to use your MID via selection of software. You can find global positioning system (GPS) apps, e-readers, movie and TV show streamers (like Netflix, HBOGo and HuluPlus), apps to help you learn foreign languages, games, music players, business productivity apps -- you name it.
Access to a WiFi network is necessary to get the most out of your device. This can be via a home WiFi router or a hotspot provided by a business. Many restaurants and coffee shops allow you to get on a publicly accessible network, but private ones you have to log into are more secure. There is some variation in what WiFi types MIDs support, with most supporting WiFi 802.11 b and g, and quite a few also supporting n. The ones that are b/g only might be a little slower to connect than the b/g/n capable ones (n being the latest WiFi standard). All are supported by most newer home WiFi routers. A few MIDs also come with Bluetooth capabilities, which allow you to wirelessly connect to various peripherals like Bluetooth-enabled keyboards and mice, or to exchange data with other nearby devices.
Some MIDs also have cellular capabilities as a connectivity option. This will usually result in a higher device cost due to monthly data plan fees paid to providers like Verizon and AT&T. Incidentally, a device's cellular capabilities often only work with certain providers due to variations in types of cellular networks and the different internal chips required for devices to access them. So, if you buy a 3G or other cellular network enabled device from one carrier and later decide to switch carriers, you may have to get a new device, or just use the old one via WiFi. The availability of a cellular option allows you to get on the Web even when you aren't near a WiFi hotspot, provided you are within range of your carrier's network. It might also allow you to make phone calls, depending upon the hardware and available apps, although you might not want to use a somewhat unwieldy tablet as a phone. Cellular also allows for proper use of GPS or any other app that needs to know your current location.
Most MIDs come with front-facing cameras (meaning facing you while you look at the screen) and built-in microphones, allowing you to use video communication apps like Skype and various voice over IP (VoIP) apps to make the Internet equivalent of a phone call over WiFi. Some also come with rear facing cameras, usually with better resolution than the front facing ones, allowing you to use camera apps to take photos with the devices.
MIDs can read a number of audio, video and other file formats, but this, too, varies a bit from device to device. The hardware specifications should list supported formats (including things like MP3, MP4, MOV, WAV or Flash for video or audio, and various e-book formats for books). But the fact that every MID doesn't support all the available formats means that there are likely some audio, video, book or other files types that won't work on your device. But to be honest, this file type compatibility issue has existed for all devices since the inception of computing. You just need to examine the specs to see if formats you use commonly are supported.
And, as mentioned earlier, the available ports on your device can affect what features you can use. They can be used as avenues for getting more content onto your device, or to connect to larger monitors and TVs and in other ways that can increase functionality. All touchscreen devices have built in on-screen keyboard functionality, but you can also do things like dock your device to a real keyboard for ease of typing.
With all this variation in hardware and functionality, continue reading to find out how MIDs stack up against each other.