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And I'm the one who's so careful with my watering!!

Oh dear Tim  :(   I hope it's not got all your crop  :(

i had a couple of toms like that - removed as soon as i saw them. i hope it's all good now :)

Yes I've had a few like that Tim.

No panic - it doesn't spread! Just wasteful.

yes, i figured it doesnt. only a couple of the toms at the top trusses had it. it has something to do with conditions at the point of setting, or thereafter?

One or two on each plant have the same here.

If, as appears from the photo, the damage is at the base of the fruit, it is clearly blosson end rot, and is usually caused by withdrawal of water from the fruit at a time when it is swelling.

Although this is often due to inadequate or uneven watering, this is not always the case.  In very hot weather it is possible for the water requirements of the plant for both fruit growth and leaf transpiration combined to exceed the abilities of the roots to meet these requirements, however wet the compost, and further watering does absolutely no good at all, and indeed may make the situation worse.

When this occurs, if the plant is a `watery` plant (i.e. one in which the osmotic pressure in the plant sap is low due to low concentration of salts in the compost) water will be drawn out of the fruit to meet the transpiration needs, and this will cause plasmolysis, or collapse of the fruit cells.  This situation arises where the salt levels in  the compost have been lowered by extra watering without the addition of fertilizers to balance out.

Where the salt levels in the compost have been maintained the osmotic pressure in the plant cell sap is higher and overcomes the hydrostatic tension in the vascular system caused by leaf transpiration and the flow of water out of the fruit is prevented.

One of my courgettes went like that - is it the same thing?

It is possible with any fruits which have a heavy water requirement, depending on the conditions in which your courgettes were grown.
It is most likely to happen where the plant`s root spread is confined and the salt level of the compost is easily reduced, as with a growbag or container, and this is exascerbated when the plant is grown in the artificial climate of a greenhouse, but far less likely when the plant is growing outdoors in an open bed and with an unrestricted root run - in the latter case the cause would more likely to be simply lack of watering.

The true blossom end rot is simply a small brown or black spot (of dead tissue)which appears at the blossom end of the fuit when the fruit is quite small, and extends in size as the fruit swells.  However, this spot often acts as a centre for the development of bacterial rots, which are what appear to have caused the damage to tim`s tomatoes and which are more commonly meant by the term.

Just to repeat -

http://ianrpubs.unl.edu/horticulture/nf43.htm