2009 Red Book.. To buy or not

Not really, the prices in those are only a baseline (or approximation) and does not always represent the current value of the coin but gives you just enough to know ballbark numbers. I like it because it has basic info about U.S. coins in a pretty compact format and how much does that info change? I typically swap out guides every three years.

The only reason I can think of is that it shows mintages for some of the coins that you won't have in your older book.

I buy several every year. I keep one hard cover for my collection and two ringed ones for around the house. Then I purchase whatever is the cheapest for Christmas Presents. Again, usually the ringed, soft cover version.
There are some really great reasons for you to buy the 2009 edition. With it you can see that Whitman still has no idea of what coin prices are. I'ts fun to look through this book for all the errors, oversights, mistakes and report it to Whitman. Proves nothing but fun. Then of course the more books you buy the more they will publish making it easier for someone to find at a flea market for $1 in the near future. One of the primary reasons to buy the Red Book is with each purchase you can look into a mirror and say I just helped some people at Whitman keep their jobs. See the more they sell the more they'll make and the less people will be layed off. Now if you don't buy that book and they lay people off that will collect unemployment compensation money, remember that is money you supported with your taxes. So in essence if you don't buy that book, you'll pay for it anyway.

I have an 08 and I dont plan to buy another one until 2010

I find it difficult to understand the reluctance to purchase a new redbook each year. The cost is minimal. You and a friend can barely go to McDonalds for less. And it is interesting to compare the books from year to year to see the changes. And there are changes. It just seems like a no-brainer to me.

As for the price info in the book, sure it is out of date by the time you get it. However it is valuable for noting trends in the prices of coins. And it is good for noting the difference in prices between coins--this coin is about double the price of this one, etc.

I say wait a year and buy the previous year's book on uber sale at Boarders for $2. Rinse and repeat each year.

I think it depends on what you use the Redbook for. They do put new things in each year. For instance the 2009 now has a section about bluebooks and their values. So if you collect Redbooks and Bluebooks then maybe you will want the 2009. If you only use the Redbook for mintages and coin alloys and weights then every couple of years is fine.