Hello David I appreciate that you have gone through Nortel Docs, but still i can guide to some points that have been missed

Nortel SMLT works in two ways
# Nortel SMLT, along with VRRP-extension #
There is no negatives to this approach as was implied in the article, we get advantage of old familiarity with advantage of Active-Active load balanced. Infact i have seen engineers love this approach beacuse of the familiarity with 3 IP concep (2 physical & 1 Virtual), this way they dont need to change their network documentation, and there is a consistency in IP-Schema in case other sites dont have Nortel Gear. Also this approach is very-very useful in case you are migrating from Cisco to Nortel, or from Nortel traditional to Nortel SMLT. SMLT+VRRP-extension has no dependency on access Switches/Servers as long as they run standard based link aggregation (802.11ad).

# Pure Nortel SMLT/RSMLT #
RSMLT provides L3 peering between two peer nodes in the Switch Cluster. Also Eliminates need for VRRP (and the need for virtual IP). SMLT/RSMLT has no dependency on access Switches/Servers as long as they run standard based link aggregation (802.11ad).

I have read the so called advantage of VSS over SMLT "that the latter appears as one device with one config file to the rest of the network". This might look like a good thing but is actually a Achilles' heel.

Let me explain. Cisco VSS apporach is very much similar to an OperatingSystem which is running on Dual CPU instead of a Single CPU. This has clear advantage in sense of configuration & performance enhancement, because the process can take advantage of both the CPUs simultaneously. The flip side is that there is a single process running across two switches. Lets take an example of OSPF, since there is a single prosess of OSPF running across two switches any failure or Maintainance (modular patch upgrade) brings down the whole system. So single control-process running across two switches gives you double the performace but looses the control plane resiliency which were available before configuring VSS.

Nortel SMLT/RSMLT approach can be compared to a cluster of servers. The servers run independent OS & processes, but are synchronized & clustered to present a single face to all end points. Using cluster approach the SMLT is able to provide Double the performance but also provides Control-plane resiliency. (infact the participants in SMLT cluster can run diffrenet versions for software).

The great minds in cisco are very much aware of the non-resiliency of the Control plane in VSS, thats the reason the primary positioning of VSS is as a distribution & access device. Core is positioned as non VSS to make sure control plane resiliency is provided.

I am sorry if i appeared as anonymous to you but i do have my email registered with NetworkWorld and you can directly get in touch with me. Infact I am parallely sending across a direct email to you with some details of the SMLT/RSMLT (and how VRRP is not mandatory for Nortel Switch Cluster - SMLT).