I hope this is an appropriate place to post this. I would like to ask you guys of vast experience your take on Allen Bradley Ethernet ENI modules. You know those little high dollar devices they sell to convert DF-1 devices like Micrologix or SLC 5/03 to ethernet. What problems have you experienced? What are your recomendations on applications? What have you learned using them? How have you coped with working around some of there drawbacks like, limited connection? Have you ever had problems with them dropping off your network? If so what did you do to resolve the issue. I know someone has figuired this out and I am too tired and busy to re-invent the wheel here. Sure would appreciate your input. 
This is certainly an appropriate place to ask. I’ve used ENI modules, but not enough to provide much feedback.
I used these quite a few years ago with a SLC/504. I remember them being very spotty. They would drop off the network just like you mentioned. I remember we rigged up the PLC to handshake with FactorySQL, and if the handshaking stopped, the PLC would drop a relay that was powering the Net-ENI, which would restart it so the comm would come back up. Yuck!
There is a much better alternative though… I forget what its called, the PLC guys around the office will know, I’ll post back tomorrow morning.
You may want to take a look at converters from USConverters. The driver will add a “virtual serial port” to your PC. Seems to be a lot more stable than the ENI’s. Just my opinion, although my opinion plus a dollar will buy you a can of soda… 
Ok, the device I was talking about was a WebPort 500 by Spectrum Controls - it comes highly recommended from the PLC guys around here.
I have used Digi One IAPs with success in the past.
RedLion data stations also work wonders for serial->ethernetIP translation. They have many more features than that, too.
Heh, it sounds like the consensus is: use anything but AB Net-ENI modules!
I have used NET-ENIs quite a bit with SLCs and Micrologicx. I have not had problems with communication between PLCs or even PACs (Logix platform), but often have problems with RSLinx correctly identifying the PLCs, especially in a spotty radio network. Sometimes this can be fixed with the latest version of RSLinx.
I have also found that setting the PLC communication channel to the highest baud rate speeds up the identification process. Turning the ENI off and on after making changes to the ENI also helps (this is true for any AB comm adapter). Allen Bradley will tell you that there may be problems with old revisions of PLCs, but I don’t know if this is true or just an excuse.
If you have the means, the Micrologix 1100 and 1400 are currently my favorite PLCs. They are very low cost ($500-$1400), very capable, expandable, and have a serial and ethernet connection. One of the AB tech support people I spoke with even recommended using the 1100 instead of the ENI.
Kyle,
Came across your post in this thread and wondered if you had success with the Digi One IAP allowing Ignition access to a SLC 5/03 using the DH485 port, rather than the DF1 port? I’ve got a load of SLC 5/03’s and they’ve all got HMI’s connected to the DF1 port. If so, which Ignition driver did you use?