I think that Costas' post(1053) was very valuable in pointing out that
there are two distinct possible ways of appropriating the surplus product
in a socialist economy: either workers are paid the value of their labour
power and enterprises get a profit which the state can then tax, or all
curently created value is paid to workers who are then taxed by the
state.
The former corresponds to the Soviet model, and the latter in some degree
is closer to what Marx seemed to have in mind in the critique of the
Gothaprogram. However, I think the phrase 'products exchange on the basis
of embodied labour coefficients' is a little ambiguous.
It could either mean that products exchange between units of production
at labour values - which would make such products commodities - or it
coul be given a more limited interpretation. It could mean that consumer
goods are distributed to individuals with them being charged an amount of
labour time proportional to the embodied labour in the product. In the
latter case, it not necessary for the products in general to be
commoditie nor is it necessary for 'firms' in the sense of legal entities
able to buy commodities and labour time to exist.
For instance, all workers could be paid by some central public body
rather than by the place in which they worked. In the latter case, whilst
the units of production might use labour time as an accounting unit - to
compare the social costs of different ways of doing things, this use of
labour time would not really be a kind of 'socialist accounting money'
since it would not really act as a means of purchase.
If labour time accounts are only held by individuals as a result of their
labour then it is not clear that an interest rate need arise. If we
assumerising labour productivity over time, one hour's labour credits
unused this year, will buy a greater amount of use values next year. Thus
the tendency of values to fall would mean that 'abstinence would be
rewarded' even in the absence of an interest rate.