I'll just put this simply: I've played scouts before.  I've never had problems.  In fact, I've never had a character die while scouting, not once, but I have made a lot of encounters far easier with decent scouting.  I've seen one scout character die to a trap, but that was level 2 in World's Largest Dungeon and that trap would have killed anyone else in the party except the Crusader had she not taken that hit, so that's hardly an argument against scouting.  So, maybe others can't do it, but I can, and have, and this whole argument has boiled down to a bunch of people saying "I can't do it, therefor it's impossible."  So instead of going back and forth on specific scenarios from a DM who clearly has no experience with this, I'll just post how to scout, because that's actually useful.  Here's the main things you need to keep in mind, and I'll phrase them for all kinds of games (high optimization and low).

1)  Be invisible to as many things as possible.  

A)  The most basic part of this is Hide and Move Silently, because everything has Spot and Listen, even if they have no ranks.  As a rule, you're only truly safe if your Hide and Move Silently, after modifiers, are 11 higher than the enemy's Spot and Listen.  That way, if you take 10 while sneaking around the enemy cannot possibly find you.  This is trivially easy... a Halfling straight out of the box gets +5 Hide, and +3 Move Silently, while a Whispergnome gets +9 Hide and +5 Move Silently.  Through in max ranks in both skills and a 14 base thrown into dex and you're looking at +11/+9 or +15/+11 even at level 1, when the vast majority of enemies don't even have spot ranks.  Note also that distracted people have a -5 to their spot and listen, and there's an additional -1 to spot and listen for every 10 feet between the observer and what they're spotting.  With these kinds of penalties, you don't even need items to avoid any chance of detection.  As you go up in levels you'll want to invest a bit of money into keeping Hide and Move Silently up, an amount determined by how much it comes up.  The Collar of Umbral Metamorphosis (22k continuous, 10k for 10 minutes per day) is great for this, providing the Dark template cheap (which gives +8 hide, +6 move silently, Darkvision and Superior Low Light Vision, and (Ex) hide in plain sight along with a few other nice abilities).  Shadowsilk Leather Armor is just 1,750gp and provides +2 to hide and move silently while also being extremely light weight (an issue for low strength stealth types), and it's not even magical so crafting it for 1/3 price is a possibility in games where that works.  There's also basic mundane gear like Silent Shoes and Darkweave Clothing that can increase both skills.  And if you're a Factotum, you even get to add your Int to it.  In the end, you should have little to no trouble keeping your Hide and Move Silently up so high that nothing can possibly detect you via Spot or Listen.

B)  Scent, Tremorsense, Blindsense, and Blindsight are all relatively common abilities that autodetect you, and you just can't have that.  Luckily, these are easily countered by taking the Darkstalker feat, which requires them to follow the Spot-Hide/Listen-Move Silently mechanic.  Since you needed those to be up anyway, this handles the problem nicely, but the feat is basically required if you want to be a stealthy character.  Without it, you're hosed... which is part of why Wizards and such actually aren't very good at this sort of thing.  No spell protects you from these things (at least not in a useful way).

C)  Lifesense.  This feat from Libris Mortis is only available to undead and causes all living creatures to glow brightly in your vision (a medium or smaller creature gives off 60 feet of light, while larger creatures double the light given off for every size category they are above medium).  Note that even invisible light sources give off light, so this sense completely trumps invisibility and no amount of hiding will save you (the enemy won't see you, but they'll know exactly where you are anyway.  They'll even see you coming from around corners).  On the bright side (heh) Necropolitans are found in this same book.  Basically, if Libris Mortis is in play, you absolutely want to be a Necropolitan (which is very useful for stealthers anyway for a variety of reasons).  If it's not in play, Lifesense isn't an issue anyway so there's nothing to worry about.  And if you do become a Necropolitan, take this feat!

D)  Touchsight.

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