Have had it working for 2 months or so now, and ran into absolutely zero issues. Just set it up the same way I did with Snow Leopard. I use a slight variation of the "golden triangle" setup.
Computers
Mixture of 10.5.8, 10.6.8, and 10.7.0
Active Directory
Windows Server 2003 R2
Open Directory
Mac OS X 10.6.8 Server
Bind information:
Active Directory first, then Open Directory. The users log in with their Active Directory account, therefore you MUST use mobile accounts. I could be wrong, but it is my understanding you can't use standard managed accounts unless they are logging in with an Open Directory account. Lastly, I reorganize the Search policy where it searches for the Open Directory server first, and then the Active Directory. Reboot, then done.
The result allows me to manage the Mac computers from the Open Directory server, while the users still log into their Active Directory accounts. My network is setup where I manage the Macs on a per-computer basis rather than a per-user basis. I have gotten it to work on a per-user basis before, but the permissions were patchy at best. But, since it wasn't really necessary for my network, it wasn't a huge loss.
Several of the Mac Pros are connected to an Xsan through fiber and a private vlan. That setup requires a master Xsan controller and a backup Xsan controller, both running 10.6.8 and both are physically separate servers from the Open Directory server. Permissions on the Xsan are managed on an Active Directory user basis (since all of my servers are dual-bound to Active Directory and Open Directory, just like my other Macs). I also have 4th Xserve machine that is running several 10.6.8 virtual machines that I use as web servers, development servers, etc.
The only thing I haven't tested yet is 10.7.0 Server. The only reason why is I haven't is because I have not heard anything regarding virtual machines and 10.7.0. Obviously you have to install regular Mac OS X Lion before you can install server software, and previously it was against Apple's terms to install a regular copy of Mac OS X on a virtual machine. So I'm afraid that means I can't run 10.7.0 Server through virtual machines since it requires the installation of Mac OS X first.
On top of this, I typically wait for the first few patches before I upgrade any servers, so as of right now the plan is to wait until December vacation before I upgrade any of my servers.
Having said that, I'm running into all kinds of stupid issues with Lion that are non-network related that will probably force me to wait until December vacation to upgrade any of my machines. (I work at a University, so the prime time to upgrade computers is during the summer and winter break.)
Hopefully that was well-explained enough to help. If not, let me know.