MAGBLAINE  I have had consistent aggravating problems with my Trash on my 15"  MacBook Pro. Twice I have had to travel the 120 mile round trip to the Genius bar at the Tucson, AZ  Store to have the trash forcibly emptied. Today I called  Tech Support and found out (In English) that my warranty had expired on my computer. This didn't stop my rep from sending me a link to the Trash It download site. I downloaded the program, installed it in the Dock and zapped the trash off to wherever trash goes when it leaves my computer.

Awesome stuff!!!!!!  
(Version 4.0)

ALEX111  I had a file in my trash which may mac (10.6) insisted was "in use" by another application. It was impossible to eliminate it. I downloaded "Trash it", dropped the difficult file on it, typed in my administrator's password (although I don't know why it asks for this...) and the file disappeared. I now have another gigabyte of free space!  
(Version 4.0)

STEVEN  Some files were impossible to delete. Even a guy at the Apple store could not explain why the files would not delete. Trash It! too the rescue.   
(Version 4.0)

SID6  The app works as advertised, HOWEVER, why did it try to connect to the developer's (presumably) server? Wouldn't have known if Norton Firewall wouldn't have caught it. I denied access, but then the app worked fine, BUT it did ask for my administrator's password before deleting. Makes me nervous that an app tries to connect to an outside server AND needs my admin password. I wouldn't use the app unless you have Little Snitch or Norton to deny access.   
(Version 4.0)

KOSOVAR1  How to get rid of 24U Appearance OSAX? Now that TrashIT! has installed it, I can't seem to get rid of it's components and they are screwing up several other apps like Vuze. Someone should have included an uninstaller. The 24U developer's website seems to give no indication of how to get rid of it. Why did TrashIt! have to install it, especially since it's 3rd party software?  
(Version 4.0)

MHUGHES  I've used this since it first appeared & have never had any problem at all. I rely on it.

To the reviewer who wanted to know what a valid administrative password is (!), it's the password you use to install any of your apps.

MHughes  
(Version 4.0)

RMENDES  I never had a file on Trash that wouldn't go away by selecting Finder's 'Secure Empty Trash' option.  
(Version 4.0)

AGENTTWEETY  The program asks me for a valid admin password. Does anyone know what it is?

Thanks.  
(Version 3.6.1)

GTMP  Trash It doesn't work. I have had the irritating stubborn untrashable file but some how managed to shift it. There is loads of advice and good freeware to shift files when they're already in the trash, easy! But, I needed something to shift a doc "in use by an application" off my desktop, this wee app. said it could do it...nope.

Now here's a thing! I've still to get my head under the bonnet with Terminal but pride myself in lateral solutions to everyday mac problems. This is my top tip, (although this does need a second mac, I was already set up for this), network an other mac to your machine with the stubborn doc. Find your way to the desktop or folder containing the doc and trash it! You get a the satisfying words "..trashed immediately..", yes please. Bye Bye.  
(Version 3.6.1)

GAVIN CUTSHALL  Works exactly as advertised, free, and fills a major hold that Apple left in the system (even in Leopard).

This one's on all my Macs.  
(Version 3.6.1)