Just been into my local IKEA and seen this deal is back and has been on a while!
From the website
Eat in the IKEA restaurant between 28th March - 30th April 2011 and we will give you the same value off your store bill when you stop between 9th May - 22nd May 2011.
Its a fine deal for those that eat in the restaurant and live fairly close, as it does mean you have to make two trips.
Make sure you get a VOUCHER and RECEIPT from the restaurant, we had some trouble last time with only having a receipt (but they sorted it out).
Remember you can also pick up sealed drinks, baby food, fruit and sweets in the restaurant. It'll work well for us as we are going to be getting some baby stuff from there in the near future