I've wanted an MP3 player for years, but could never justify spending more than about £30-£40 on one; An iPod was out of the question.

The display is not a glamorous 320x240 colour screen, but at this price you can't expect it.
Instead, it's a 4-line organic LED display - top line yellow, the other 3 blue.
The circular control-pad is also illuminated with a blue LED ring (though thankfully only for a few seconds).
With this control pad, you can choose Music, Settings, or Voice recording (this model doesn't have the FM radio), and navigate the menus.

The obvious competitor to this player would be the iPod Shuffle.
Now the new Shuffle looks cool, but is more expensive that the Clip, and has no screen.
Because of the screen, the Clip can have navigation controls, Album/Artist/Song selection, EQ, and a battery life indicator, none of which (obviously) are available on the Shuffle (or the Zen Stone).

Plugging the Clip into a PC makes the Clip's memory appear in My Computer under "Sansa Clip 1GB". You can copy music on there using the Sync feature in Media Player, or by copying the files onto the clip directly.
One possible source of confusion is that there are two ways to connect an MP3 player to a PC: MSC and MTP.
The Clip can use either mode (as can Media Player) but files copied in one mode are not visible (from the PC) when connected in the other.
My advice: choose one or the other (MTP or MSC) and stick to it.

For me this was no problem - I already have an Aliph Jawbone, which comes with a USB wall-charger; it produces the 5V (like all USB chargers should) that the Clip needs.
And in any case, I use a PC often enough that I wouldn't have a problem leaving it on for 2-3 hours to charge the Clip.

ID3 Tags

The Clip doesn't work this way.
You can arrange your music into folders on the Clip's memory, but the Clip itself doesn't display that arrangement. It sorts everything into artists, albums and genres, and that's how you browse your music on the player.
To do this properly, your music needs to be tagged with the correct artist/album/title/tracknumber info, otherwise your music will disappear into an album with the catchy title of "Unknown".
If you're converting the music in your CD collection,
Windows Media Player will generally Do The Right Thing, but if you use other sofware, or you have acquired your music by dubious means, then you may experience problems.

But techies like me love this stuff, and will also love the fact that you can apply firmware updates without turning the device into a brick.
(Sony Ericsson and Tom Tom, are you listening?)