It is useful to know both the supply and return water temps. On my radiant floorloops, it is set up for 130-degrees on the supply side, and right now (about 18-degrees outside), it is about 60-degrees on the return (this varies depending on the heat load). Note, some boilers are not designed to allow return water this cold.
A good circulator pump is nearly inaudible in most situations, at least on the ones I've played with (limited). If it is very quiet, you can hear them, or feel them slightly. Vibrations or noises may indicate cavitation (not good!), air pockets (also not good), or a bearing starting to go. Note, these use a water cooled/lubricated bearing - running them dry will ruin them quickly. Many circulators don't have much head (the ability to pump against a load - normally figured as rise). A closed system (one full of water without any air pockets) is much easier to pump than one with air. ANy air pockets in the line can prevent the water from flowing.