The monorail is okay but it all depends on where you are going and what hotel you are staying at. Do a bit of research map out where your destinations are relative to the monorails, otherwise get use to walking, even if you are taking the monorail.
1 way is $5, unlimited all day pass is $12 and an unlimited 3 day pass is $28. yes, way cheaper than a cab as going down the strip from the Palazzo to the Paris hotel cost $10 and it was a very walkable distance.
The monorail doesn't run to the airport and the stations aren't located close to the hotels - mostly due to the cabbie opposition. If you happen to stay at a hotel where there is a monorail station, then you save yourself at least 10 mins of walking. I stayed at the Palazzo and it was a good 15 min walk just to get to the Harrah's station. Just remember the hotels make you walk through their casinos in order to get to the monorail and casino floors aren't exactly a quick walk through.
The monorail runs to the Las Vegas Convention Centre BUT it's situated at a distance away from the convention centre, as it's closer to the South Hall. So it's like parking at the far far end of a large shopping mall and having to walk in from there - okay on a nice day but when the elements are working against you, it sucks. But a cab ride from the convention centre to the Palazzo was about $9-$12 depending on the time of day. So if you have more than one person, then a cab isn't such a terrible alternative if you hate walking. But say you're at CES and everyone wants a cab at the end of the day, then maybe the monorail isn't such a bad idea.