I've actually been looking at trying CFL's in my "new" Elwood 5x7. It only became operational last weekend so I've got lots of experimentation that needs to happen before I can say definitively but here are my thoughts right now.
The assumption I think most people make here is that near absolute consistency is expected from their enlargers; as Mick says (and he is right) if you need 10.4 seconds exactly to do the job you are trying to do, I concede that that may be tough with a CFL.
As a newbie to enlargers, I don't have that "10.4 second exactly" expectation.
The issues with CFL's seem to be:
1 Warm up time.
2 Shut down time.
3 Losing intensity over time.
(4 If there are others I'd like to know)
The pluses of CFL's for me:
A Low heat, I don't want to cook the negatives. From what I have been told the original 500w incandescent bulb in this Elwood required several layers of heat absorbing glass. That glass is missing from this unit now.
B Better diffusion, the Elwood can have a significant hot spot and the larger light source seems to give me a more diffuse pattern of light.
C I can choose the color temp of the bulb I use for any given session, for effect, just like I can choose filters.
Okay, on to the issues
1 Warm up:
The advice I've received and experimentation I've done so far seem to agree; if the bulb is warm to start with, then it will come to full brightness very quickly (without flicker).
So my plan is to keep the bulb on during focusing and while I'm setting up and between runs. The flicker/slow start issue becomes moot.
I'll just turn it off before I load the paper, turn it back on when the paper has been in the fix long enough to be safe, and then leave it on until I'm ready to load paper again.
2 Shut down:
This is a little fuzzier but both my Elwood and my Omega have red filters that can be put into the light path quickly after the exposure. I was even thinking of using an opaque something in place of the red filter or just tossing a sheet of old paper over the freshly exposed sheet.
My second thought here (and this would mitigate the warm up issue some too) was to make that my exposures longer. Instead of the 10.4 seconds I might use with and incandescent, I might stop the lens down one stop and use 20.8'.
With the longer total time; warm up and shut down issues become less significant. This also gives me more time for dodging and burning, a big plus given my lack of experience.
3 Losing intensity:
I can see where this could be a problem in creating consistent proofs over the course of a year.
The fixes are so easy though that I don't care.
Just change the bulb every few months (put it into service somewhere else in the house) and/or do a quick test strip once in a while.
For prints that I'll be spending real time on, a test strip for that negative is not something I'd want to skip anyway and the intensity should not vary that much in one session. (Given a reasonably consistent process plan.)
I, like some others, use replenished developer for my film and it has been quite consistent but sometimes it needs a tweaking. The temps I develop at (film and paper) change depending on the season. Sometimes I goof on my camera settings.
My point here is that there are many inconsistencies in the processes most of us use.
The only thing that the enlarger bulb needs to be is predictable, if we factor the problems into our system we should be able to get reasonable results.
Also, for me, camera work, developing, and printing are each "expressive arts" not "production runs".
I don't necessarily expect or want any two prints to match.