Its sounds a bit vague, but how steep is the learning curve when moving from solaris 10 to RHEL?

This is pretty hard to say. There isn't any definitive answer to this. It depends on a great number of factors, such as how much experience you have, how quickly you learn, how really you're willing to reach out for help, etc. Every linux distro is different. With that said I would have to say that if you're fairly good at getting around Solaris you will be fine with the switch if you work at it. RHEL has pretty good resources out there, so I'm sure you could probably manage. If you have any specific question let me know and I may be able to help you out.

Well I'd say there's likely to be a bit of effort involved.
Going in the opposite direction, I keep trying to get interested in OpenSolaris, but all the tools I know are different/missing. I have no imperative to stick at it, so I keep losing interest. If it's work, I guess you'll have some incentive ...

Yeah, it kinda feels like a downgrade. I am used to thinking in c0t0d0s0 . Actually we have an entire SPARC/Solaris environment here. But ever since this oracle/sun merger started, prices and gone up and support level/service has gone down. Some are entertaining the idea of moving to RHEL.
It will take at least an year, even if the port is approved. Well, I think I will ask for training,...
On the brighter side of things, I will get quicker replies on forum,.....

I'm more or less looking at the opposite; a lot more exp with RHEL than Solaris.
RHEL config at the admin level is simpler in several ways, eg networking involves less files.
The Admin guide is here: http://www.linuxtopia.org/online_boo...ion/index.html
Install guide: http://www.linuxtopia.org/online_boo...ide/index.html
Note that Centos is a free re-build of RHEL, so you can download that and practise and it's alomost identical for the same versions eg latest RHEL 5.5 = Centos 5.5.
The main differences are Centos has to replace the proprietary RHEL logos, splash screen and remove the RHN update daemon.

I am assuming (and hoping) that with this merger oracle will take its market away from Linux and will focus on its own O.S Solaris/openSolaris.
The pictures isn't very rosy right now, with all the issues Sun customer are having, but once the dust settles down, that is the logical way to go.

CENTOS = RHEL -> thanks. Didn't know that. Shouldn't fedora be similar to RHEL, since its kind of like a community RHEL?

Fedora is a RH sponsored project but it is not exactly same as RHEL. The code base is definitely different. Fedora though works as a test bed for RHEL for cutting edge technology which when rock solid is put into RHEL. But CentOS is almost RHEL without trademark logos and such. It is compiled from the srpms from RH.

I agree with chrism01 - I actually did the move from Solaris 9/10 to RHEL and I've found that RHEL is much easier to administrate than Solaris. A lot of things are simpler and better documented (your trusty friend Google would be key).

There is a bit of a learning curve that you'd need to get through; in order to get familiar with the differences between the OS's.

re Oracle; don't forget that OEL (Oracle Enterprise Linux) is a rebuild of RHEL, though not free and (I believe) heavily tweaked to run the Oracle DB.

As above, Fedora is the R&D distro (free), sponsored by RH; bleeding edge stuff and a new version every 13(?) mths. Don't even think about using it for serious work.

Regarding OEL, I'd advise people to stay away from it - chrism01 is correct in that its heavily tweaked for Oracle DB EE.

However, after the Sun acquisition; Oracle is touting Solaris as "the best OS to run Oracle" - so I don't have much hope that OEL will last much longer (I'd be surprised if they rebuild RHEL 6 when its out).