First I would keep in mind that single family homes values are not falling all that much here in the St. Louis area. Despite the national news of housing markets being off by double-digit margins, home prices in most part of St. Louis have declined very little if at all from last year (small single digit decreases). In fact, in most areas in the metro area the number of homes sold through this point in the year is very similar as well.
What we have seen is an increase in the days that homes are spending on the market. This is simply a function of the high inventory of available homes. This inventory has been created by many factors and the credit crunch is certainly a contributor. The number of people who purchased homes that were out of their price range over the past few years means that there are more foreclosures, and more people who are looking to get out of homes that are too expensive now that there ARM has adjusted.
Now, how does all this effect multi-family homes? Well as you will see on my previous answers to this similar question, holding income producing multi-family property right now is a very strong position to have. Right now there are also many good buys in the multi-family market. With more people needing rental units over the next months and possibly years, you would be smart to get in now while prices are still relatively low. Again, do your homework, analyze the property, work with a professional who has experience with investors, and use common sense. Another thing to keep in mind is that many experts are saying that the St. Louis market will be one of the first to "rebound". There is a good article about St. Louis on cnnmoney.com