I've had both. The Terroc is basically a beefed up flyroc, slightly stiffer midsole and although not an out and out fell shoe, more geared up for hills. The uppers are more robust than the flyrocs which admittedly are pretty light weight in that department - I ripped mine to pieces before the soles had shown much sign of wear.
I also have mudclaws (for fell mainly), x-talons (xc races) and roclite 295s. I don't get on too well with most of the roclite range but the 295s are great - quite similar in feel to the flyrocs but again a little more robust. These have now replaced my flyrocs/terrocs.
Also consider, Mizuno Wave harriers - cheaper than inov-8s but certainly comparable to the flyroc. I'm on my 3rd pair and the only downside I've found is they absolutely stink after a month or two - nothing to do with my feet, I'm sure!
Edited: 01/10/2012 at 13:18