haha I bought £2000 in each about 6 weeks ago, and I'm down about £500 on Tesco and £400 on Sainsburys. Twitchy bum time indeed but I thought they were about as low as they could go then so I hold no pretense that they are low as they can go now.
At the same time I bought a similar amount in Imagination and ARM, and only ARM has stayed stable.
I have another £7k in funds though which are all doing OK.
I'm in for a while yet though and fundamentally I think both Tesco and Sainsburys are strong businesses (especially Tesco ironically, which has much diversity).
I think they both got caught out by the rapid growth of the discounters [and arrogance], what they need to decide and decide quick is how they counter that. I think a mix of aggressive price cuts (maybe even a bifurcation of their physical business into discount stores and normal stores) and an aggressive cut and sale of some of their physical locations will put them in good stead. One advantage both have is extremely large property portfolios so they don't lack the means to be able to generate revenue for aggressive restructuring and investments.
I also have a sneaky feeling that there is a lot of hype around the discount stores and sooner or later this will die down and shoppers will return to "normal" shopping habits.
But I would say all this wouldn't I