First off, the scout is the fastest class in all of TF, but also comes with the least armour, 50 at max. The scout's arsenal and properties have been designed to give the scout as much of a speed advantage as possible.

Weapons

The scout is the only class carrying the nailgun (Alongside the normal axe and shotgun), which is annoying at the best of times, though can inflict some worthwhile damage on static or slow moving targets. The amount of ammo a scout can carry is low as well, 200 nails can easily be used up if you don't pay attention on your inventory.

To compensate for having low armour and light weaponry, the scout comes equipped with 2 "annoying" grenades in the form of the concussion grenade and caltrop canister. The first simply blasting any players nearby, including yourself, out of the way and making them concussed. Medics can cure the cuncussion easily.
The caltrop canister drops 6 spikes (caltrops!), which hurt players slightly and slow them down until being healed (by a health box or medic).
The caltrop canister has replaced the flash grenade since TF version 2.8, and does a small amount of damage to any players nearby, as well as blinding them temporarily.
 

The Motion Detector

Scanning is very useful now in TF 2.8 and all versions thereafter, as it now gives you quick info on the position of players and what class they are, and can be switched "on" or "off". Scanning uses up cells, which the scout can hold 100 of. HOWEVER, for some reason, when Valve re-wrote TFC they decided to leave the scanner out. So no scanner in TFC :(

The commands to use in 2.8 is simply "autoscan", however these older commands will still work and change the range of scanning:

scan10 - uses 10 cells
scan30 - uses 30 cells
scan100 -uses 100 cells

I recommend using the "special" command:

special - same as scan30

If you wish, for some strange reason, to change the team your scanning for use:

scane - detects enemies
scanf - detects friendlies

Spies And Detpacks

No, the scout can't lay detpacks, but diasrm them when set by a demoman, just stand over it and look down at it to start. You also get 1 teampoint for this. Similarly the scout can also detect undercover enemy spies by simply coming into contact with them. You also gain 1 point for this each time.

There is a bug in the current TF code however. It is possible to set a detpack for 255 seconds, which is effectively permenant, and when placed in awkward positions become impossible for a scout to get past without diasrming(which takes several seconds) and isn't good news if said demoman is near.
The best way to get round this? Complain like hell about cheating and hope no one does it again!