I actually think the Scout is balanced pretty closely in comparison to the rogue. The skirmish ability doesn't require flat-footed, flanking, etc etc to pull off--but is balanced by the fact that it's basically limited to a single attack per round. Hit dice are d8, and they get some ranger-like abilities, as well as losing the rogue's Cha-based abilities and gaining some ranger skills. (Which could be considered a benefit because you can junk Cha then.)
The issue I have with the Scout isn't about balance; it just means that the rogue is still *required* if you need to disarm traps. And this stupid, lame, mindless, HORRIBLE rule is bypassed just by taking a single rogue level. Bam! The 19th bard/1st Rogue at least can now disarm traps etc etc just like a 20th Rogue. (Edit: Assuming of course, they pay the cc cost. I houserule bards having those skills as class skills too though--which is another debate entirely.

Which is utterly, mind-numbingly STU--
Sorry. Resetting my rant.
Anyways, for the above reason, I houserule in my campaigns that bards can use those skills just as well as a rogue (assuming they take the skills of course.) So I would also houserule that the Scout has Disable Device and Open Locks as class skills.
NOT as a balance issue--but simple to give players more options when a 'thief-type' char is needed.