We had the bonded line offering from TC from February through October last year...when it worked it was good but doesn't provide the fantastically awesome speed one would expect (especially considering it to be a '20mbps' connection), I downloaded files faster over my 4mbps ADSL line at home using a regular 3GB saix account (and substantially faster at that and way more often than the bonded line ever downloaded fast). The lines went down often and the service was unstable with an uptime of 50/50 with our site often been made out to be the problem whereas I never have/had these issues with our IS uncapped router.
In 1 scenario, I setup routing and remote access on a 2003 server for VPN functionality, with a static IP with our IS ADSL line, worked 1st time every time with many clients, connected 8 laptops (all that I had in the server room with me at the time with 3G cards). Replace the IS connection with the TC bonded - I could get the first VPN connection (but not 100% or anywhere near there either) but getting anything more than that was virtually impossible sometimes taking 20 attempts to get a connection - maybe. I was told to setup multiple static public IPs to the server and this didn't make 1 difference to anything.
And how is this for stupid too...their equipment was delivered without a power cable, without details about what our static IPs were or what DNS servers to use or what (I know I refer to IS a lot but in my experience they have really good service - when you get an uncapped ADSL with IS they preconfigure the router, print out the range of IPs allocated to you, what DNS servers to use and the name and direct line number of the person who setup the router in case there any issues). The guy delivering the equipment wasn't of much help either and when phoning the TC office no one even seemed to know that they were offering public IPs with the bonded line. To top it all off, it only has 1 ethernet connection, so you get 5 public IPs but you have 1 ethernet interface? So you must now plug this into a switch and then distribute from their to the various servers you want to connect via public IP - connecting to the switch was considered a problem by TC many a time too. Slightly unrelated but still a reflection on TC's service was that their DNS servers were slow especially with dynamically updated IPs, one could often wait hours before their DNS servers updated whereas on the other side with the IS ADSL it was done more often than not within minutes.
One positive thing to say is that you could punish the line by doing multiple downloads/uploads etc but you could get a relatively consistent latency through out.
I don't post this to say that it is a bad idea but these were my experiences with TC's bonded line offering when we used it last year - I was very hopeful of the technology and just want others to know the facts and go in to something like this with their eyes open.
Oh...and 1 last thing, the bandwidth on the bonded line was hellishly expensive (over R5k for 40GB!!!!)