....to merge all the cuts I've made on brushes so I can get under the max cell count problem I'm encountering when compiling reflections? I have a long catwalk in a warehouse, the grating has elongated octagonal slots and its made for alot of very small seperate brushes after cutting the slots in the steel plate. I can change it to a standard mesh grate or something, but I'd like to be able to keep it as-is and merge all the cuts to keep it as authentic as possible. Thanks in advance.

Ctrl+U still works. But you 'Cannot add a set of brushes with a concave hull.'

Thanks for the reply, I'm learning the functions as I go, that helps greatly, & hopefully will get the cell count down considerably. =D

Just in case you were wondering, here is a concave hull;

Right, the slots looked much like the "v" notch there, except it was a "u" with the bottom corners cut at an 45-degree angle on each end....like a stop sign with the sides elongated. With the number of slots in the diamond plate catwalk, there was 7 cuts at each end of each slot there was thousands in that catwalk alone. Btw....what is the cell count limit, anyway?

A little off the question here, but did you make the parts to your catwalk Detail? I had a very similar situation, exceeding max cel. I had built a stair well and forgot to make the parts detail. Once that was done, no more problem.

No sir, just the default brush type...structural. But the number of cuts I made created 14 brushes for each slot & resulted in thousands of brushes. Hope you find out what causes your problem. The other map editing program from which I'm taking the measurements of the map uses a combination of spacebar & left mouse button to rotate the camera. When I minimized & switched to radiant, I had occasions where that resulted in cloning objects I had highlighted because of the temporary confusion of controls.

So to clean up your cell usage just make the catwalk parts detail

Ok, thanks. What I went ahead and already did was just make the whole thing solid diamond plate. I will keep that in mind next time when I encounter a similar situation. I've never made anything detail before, does it still remain solid? And what's the pratical difference between an object left structural & one left detail?

Alright, you need to read up on portaling, cells, viz and such here in the forums. Also there are lots of threads structural and detail.
I am not going to go into a detailed description in this thread, but basicaly if it is something that is not going to totaly block the visibility (viz) of an area you should make it a detail brush. Detail brushes do not block the games engine from rendering viz of things behind it when the player is looking at. The thing is, if the area the player is looking at is not completely enclosed by structural brushes and portal brushes the the engine renders everything there anyway.

It is a tough concept to grasp, at least it is for me. I am still working it out myself. But there are plenty of resources here to help with it. Don't just restrict your searches to COD4, use the other forums as well. Many of the concept still apply.