RR - it's not that machines didn't work for me it's more a case of they worked well for an initial period of time but then progress slowed and my personal trainer moved me in to free weights. So it's not a case of not working or being to easy, more the case of core strength... When you lift something heavy in real life, you don't just use that primary muscle you've been training but also many others to stabilise the load. I also found that with free weights my progress accelerated again, having stalled somewhat on the machines following my initial progress. Another to consider is that Abs aren't build on machines or using Situps and crunches, in reality they're build from core moves as the body uses them to stablise as mentioned previously. Having said that of course they're still eluding me

BUT they are there just not visible, diet is still the issue for this former fat boy (abs may be something you already have or are not really interested in)
Calves, again depending on what you're training for, calves are hard to develop so a lot of people would train them for hypertrophy I.e. 8-12 reps OR combination of strength and hypertrophy (5-8 reps) - 20 reps would be training them for endurance and would be my preference since in my case I have substantial valves, and really what I need out of them is stop getting injured during long runs or periods of intense training for martial arts.
With regards to "effort" I would say you should always be failing on the last two reps of the final set, whatever rep/set range you choose, but the number of reps vs. sets are specific to training goal.
Going into gym now, they've just opened the door!
Let me know if I've missed something, remember mate I'm no expert but done a heap of reading and found what worked for me.. There's literally hundreds of different views out there and probably more than 50% all work to a greater or lessor extent - trial and error my friend, if it's working go with it, if it stops working change it - simples!!!
Edited: 20/12/2011 at 07:35