Kambing, just a quick post to acknowledge your response, and thank you for your comments.
Although I still think that throwing 'gift' and 'present' into sharp relief as an aid to political understanding is useful, I'm leaving the thread now due to unwanted attention, so I won't elaborate further. Thanks again, and feel free to criticise my thoughts further.
The problem with this is that there are many forms of exchange that combine these two types of relation in ways that mean that this simple dichotomy cannot really be sustained. There are also ways in which the various kinds of 'presents' or 'gifts' share key qualities that differentiate them from eg. commodities. I do agree that, unless one is discussing 'gifts' at a rather high level of abstraction (i.e. in terms of general processes of objectification, or in terms of a generic contrast between gifts and commodities oriented towards an analysis of the commodity form), the category of 'gift' needs to be unpacked into much more specific forms of exchange relation. But I don't think you'd end up with a binary of 'gift' vs 'present' if you did this.
Still, given that we live in a commodity-dominated society based around processes of alienation, the category of 'gift' serves a certain contrastive function -- even if it is by no means synonymous with egalitarian or communistic relations.