i collect money from tescos, waitrose, Asda, etc - (and i have to say their new edi supplier systems are vastly better than the pre-existing systems, if that's what you do for them Orm...some of those were so poor they put people out of business by non-payment.) If Orm ever wants to work for a faceless multinational bank instead, I'll definitely put in a word (and collect me £500 bonus for doing so!)
and yes they do screw their suppliers a bit - though their contracts can qually keep a company afloat...so a mixed blessing.
the very good thing about trading with tescos is, you know they won't go bust before they pay you. You might, but they won't.
lets face it, supermarkets are great - that is why they are so successful. People go on about local shops etc - and a good local shop is a gem, but all too often - irregular opening times, limited range, high prices, shockingly rude and intrusive service - made them a crap option.
and quality of food wise, supermarkets actually apply fairly stringent standards to suppliers (appropriate to price bracket of course) which some small shops are simply not in a position to do.
and why do we get angsty about them on Mumsnet? well, supermarket shopping is something most of us do, and fierce competition between the big 4 has upped customer expectations considerably. we expect alot and every time go shopping is another opportunity to be disappointed!