are you referring to research analyst upgrades and downgrades? If yes, then the usefulness of this falls on the shoulders of the analysts and firms they work for, not the website publishing them. Right?
Or are you referring to stock grading websites that are not (re-) publishing Wall st. analysts ratings? If so, I know of a few high quality ones aimed at investors rather than traders. Stockgrades and ValueInvestors and magicformulainvesting.com are a few of that type.
As for the repackaging (of Wall St research) sites I have some advice. I have been tracking Wall St research for several years as an input to a multi-factor trading method. Using simple upgrades/downgrades and new initiations alone is not good enough but its good used in conjunction with of a strategy using price patterns, volume, market conditions, calender effects and such.
Briefing.com used to be good before the major Wall St houses denied them their rating change information (you won't find Goldman nor BofA/Merrill there any more). Streetinsider has comprehensive data but just recently went from free to a subscription service.
I currently use theflyonthewall.com which is a paid service and I use a bit of MS Excel trickery to develop a database of information which I do not share! (in case theflyonthewall tunes in here).