For the past 3.5 yrs I've been using the CANON PIXMA MP990 Multi-Function Printer/Scanner to scan my 40-yr old 35mm slides. It has been fantastic!! I use the little adapter that came with the device. The only drawback is that the MP990 scans only 4 slides at a time. Nonetheless, I scanned 126 scanned slides this way, importing them to iPhoto, and then saving to a DVD for a photo show. It wasn't bad, really. You just get into a groove. The quality of the scans is super, but YES you need to photoshop each image (remove tiny specs and improve color saturation). It was fun to revisit each image and see it looking good once again.
However, this week my MP990 is on the blink. Nothing to do with the scanner... that function still works great. Something is wrong with the BGBK black ink cartridge read out. Rep says I probably need to buy an entirely new machine. I was considering the newer MG8220 (has ability to scan slides), until I read about the auto-cleaning function which uses up TONS of ink... and there's no way to prevent the 8220 from NOT auto-cleaning. Boo to Canon for that.
My advice: If you can find a barely used MP990, go for it. Fantastic scanner of 35mm slides AND negative strips.