The Quiet Competitor to the Heavyweights

The IAUDIO X5 is not a MP3 player your average consumer has. Its not been marketed to anything like the extent of Apple's iPod. It has relied on word of mouth, and its loyal fanbase that has tracked the developments of Cowon's product lines over the years.
My experiences are based on owning the 20Gb model since August 2005.
The X5 is beautifully crafted - very slim, a distinct lack of buttons and a sleek black finish.
One of its biggest selling points to me was its unmatched format support - Ogg Vorbis compatibility was a must for me, and instantly limited the selection of MP3 players to a tiny number. In addition, the X5 plays other more common formats - MP3, WMA etc. with no problems. Please note, however, that the player does not as of yet support DRM. From a moral perspective I actually considered this a selling point, and found it encouraging that Cowon are not so desperate to jump on the rights-grabbing bandwagon. However, some recent beta firmware builds have experimented with DRM support but is not at a stable release yet.
Although the X5 supports images and video on its very lovely colour screen, I don't feel that either have been implemented very well. The pictures viewer suffers from a clunky interface for navigating them, and it's rather slow at loading each image. The ability to zoom into portions of the image is welcome. Video must be prepared in a certain format, and is limited to 15 frames per second. I've found that this generally works very well for animation, but movies, music videos etc. will stutter badly during high action or rapid camera movement.
For those of us who haven't quite arranged our digital music collections into formal folder hierarchies, you may be surprised to learn that the X5 does not yet support a tag database, to allow easy searcing by artist/track etc. This, in my opinion, is a very unfortunate weakness of the player, but Cowon has long promised a firmware update in the future that will add this much-wanted feature. Be sure to look for software that can help monitor and sort your collection into artist>album>title structures.
The X5 is one of a very select few that allow some sort of customisation. If you download pictures onto the player, you can select one to be the background for the main player interface. Generally the interface is easy to understand and navigate, but it lacks the smooth fluidity of the iPod.
The 4-way joystick, which the majority of navigation is done by, feels sturdy and reliable, and is unlikely to be accidentally pushed whilst bouncing around in your pocket - hold functionality is available. To charge via power adapter or USB cable, a supplied sub-pack is connected to the base of the player. This does mean however, if you lose this, your player is going to be of limited use. Although Cowon offer some software, it's usually much easier to stick to your own choice of synchronisation software, or good old dragging and dropping between explorer windows.
Rarely for an mp3 player, the X5 includes a USB Host port. This allows it to be connected to certain devices, such as digital cameras, so that its pictures can be downloaded directly onto the large-capacity drive without any need for computers. For snap-happy holidaymakers, I imagine this feature could be something of a godsend! :)
Part of the X5s appeal to its fanbase is its somewhat rebellious streak. Cowon could've chosen to release a fairly generic player that did the same as every other iPod clone. Instead, they've taken some changes, taken the restrictions off our own media, and produced a reliable, beautiful device. Although it has some quirks which may irritate some, its most important job - playing music well, is handled brilliantly and there's lots of scope for playing with EQs, bass and 'enhancements' that personally I like to leave off.
One warning though - as with many music devices, the stock earphones are nothing special. If you're just trotting around town then you're unlikely to care too much, but within a few months mine were beginning to fall apart. Also, be sure to explore the cases available. The X5 is a small investment - don't let it be ruined by stray keys in your pocket!