We've got a leased line too, only advantages I can figure out is that its guaranteed, unshaped, and unlimited usage.
But yeah, like

expensive, our 256K line comes in at R13K pm!
So, unlimited yeah, but only 256K... we need faster but going 512K puts it over R20K per month. no way hosay!
But I see new technologies coming up... one company to come see me is talking about a wireless link from Randburg (about 30Kms away, we're in Lanseria), gauranteed 1Mb speed (minimum, many times faster), at about R6K/pm... we'll see.
Another option is maybe get ADSL and use that for the fast needs (eg. video conf), keep the leased for other usage (mail, normal browsing, downloads, etc)... but the prob there is Telkom (kom nie!) with ages long installation of ADSL in the area, same old "no port available at present" ****
I must actually check whats our bandwidth usage... no use paying a cr@pload for unlimited usage, and s-l-o-w speed, if we can get much faster speed, even if limited to maybe 30Gbs.
But then theres also the stability and latency... my experience with wireless (iburst/mtn/vc) is not good vs fixed line....