I used the trial a while back and it worked well, unfortunately I didn't have a apple remote at the time. I finally got an apple remote and reinstalled RB onto my macbook. 
I followed the tutorial to a "T" for getting PLEX set up with RB but I could get no response in PLEX. I thought maybe it was a setup issue as it would not switch the active behaviour to PLEX. I forced it to start up with PLEX and still no go. So then I set a global command to activate frontrow, but still no go using the original apple remote.

I know RB is seeing the commands b/c you can watch it switch around to the different virtual remotes when you push buttons on the Harmony. 
Everything works normal with RB shut off.

Also, Mapping is showing 2 PLEX icons..how do I remove one of them? 

As for the "no response" problem: 
Please update Plex to the latest version, where the Plex team fixed 
this bug in Plex. You can also find a discussion and a detailed 
analysis of mine along with a proof-of-concept code in the "Plex 
Version 0.5.14 problems" thread in this forum.

If you see two Plex icons in Prefs > Mapping, there's two 
possibilities that I can think of:

1) You have several different versions of Plex installed. RB ships 
with two different Behaviours for old Plex versions and new Plex 
versions. Thus, if you have several different version of Plex 
installed, you'll see both Behaviours - one for the old Plex versions, 
one for the new Plex versions.

2) You have created your own Behaviour for Plex. You can remove that 
Behaviour at 
~/Library/Application Support/Remote Buddy/Behaviours/

Best regards, 
Felix Schwarz 

I do have the updated version of PLEX (0.5.18 I believe), this is the only version of PLEX that has been installed on the macbook...I had the old XBMC version on it until this past weekend...which I decided to update since I finally got the Apple Remote.

I did create my own behaviour for PLEX, this will probably count for the 2 icons.

I also tried something else, I paired the apple remote to the macbook and set up the global commands to make calls in Frontrow instead of PLEX, just to make sure it wasn't a PLEX issue and the Apple Remote won't control Frontrow at all....again, everything works fine as long as RemoteBuddy is not running.

 
Last edited: 16.09.2008 08:05:15 

Please make double sure you are running the latest version (by i.e. 
making a fresh download and replacing your current version with that 
download), because older versions of Plex do have the exact issue you 
describe. You can find more info on that in aforementioned thread, and 
an acknowledgment of the problem by the Plex team on their forum as 
well as user reports reporting the problem with an older releases of 
Plex and that all of them see it fixed with the latest release.

I'm sorry, but I don't understand your last sentence. If you mean that 
you set Remote Buddy to emulate Apple Remote presses and that these 
are not picked up by Plex, but are picked up by Front Row instead: 
This is another known problem of Plex, not of or with Remote Buddy. 
I've been in touch with the Plex team about it, looked into their 
sourcecode, looked through the source, identified the problem in their 
source and sent them both instructions how to fix it as well as a 
complete set of sample code on how to use the Apple Remote Receiver 
correctly. You should see these fixes in upcoming releases of Plex.

Best regards, 
Felix Schwarz 

To do this, I did not set up a behaviour, I simply Paired the Apple Remote with RB and then set Global commands to Activate Frontrow, etc...

I did this to rule out issues with PLEX. 
I will try to reinstall PLEX tonight, just incase the About PLEX is lying. If this doesn't work, I'll completely delete the PLEX behaviour I created and try to set up a behaviour for Slingplayer..to see what this does.

Again, I don't think it's an issue with RB or PLEX, I think it might be something I'm doing wrong or missing. 

RB will not transfer the codes to PLEX if it is set up to use multiple virtual remotes. If I turn the multiple remotes off and only use RB with a single code, it works fine.

So then I set it up using my BD remote, everything works perfect.

I need it to work using multiple remotes so I can use my harmony instead of two remotes. 

If you created your own Behaviour and you previously had OSXBMC, 
chances are your keystroke actors are not pointing to the correct or 
an invalid bundle identifier. The bundle identifier changed between 
OSXBMC and Plex. It's now com.plexsquared.Plex

I can ensure you that Remote Buddy will execute all actions in the 
same way regardless to which remote they are mapped. The driver part 
(where multiple remote support is implemented) is independant from the 
handling part (where actions are implemented and executed). There are 
no intersections.

I recommend you a start with fresh settings. Therefore, quit Remote 
Buddy, move all settings from

~/Library/Preferences/com.iospirit.remotebuddy.*

(except those matching ~/Library/Preferences/ 
com.iospirit.remotebuddy.com.apple.*)

and all Behaviours from

~/Library/Application Support/Remote Buddy/Behaviours/

to a new folder on your Desktop, then start Remote Buddy again. Then 
go to Prefs > Mapping > Plex and map Remote Buddy's Plex Behaviour 
actions to your buttons.

If such a fresh start with fresh settings doesn't help you:

There has been a known problem in Plex 0.5.14, though, which meant 
that it doesn't handle short keystrokes correctly/at all, even though 
it has already received them. You can find in-depth information and 
details on this issue in Plex in the "Plex Version 0.5.14 Problems" 
thread and also in the Plex forums.

If you are running a later version of Plex and you still experience 
that problem with the Plex Behaviour that ships with Remote Buddy, 
please contact the Plex team as they are the only ones that will be 
able to help you further.

Best regards, 
Felix Schwarz