I'm sorry to say that mosts of the posts on this subject are incorrect.  Here's the difference between a manufactured home and a modular home.  A manufactured home is built according to the HUD code.  When reselling, it has to be compared to other manufactured homes to come up with an appraisal.  Just like stick built homes, some manufactured homes are better than others.  It depends on the manufacturer.   It is true that manufactured homes do depreciate in value.  However, they are a viable option for many people.  I have customers that have lived in Manufactured Homes for 25 years and trade them in to get a new home.  In the country, this is quite common.  If you take care of them and they are a well built home, they can last just as long as a stick built home.  If you don't take care of them, they won't last long but neither does a stick built home.  I am a former realtor and have seen many stick built homes that are falling down.  Why?  Neglect by the homeowner.  My husband and I have owned 3 stick built homes ranging in price from $100,000 to $275,000.  Some were built better than others.  We are now in our late 50's and plan to purchase a manufactured home in the next 6 months.  Why?
1.  We have family land
2.  We want something that we can get in quickly rather than being built
3.  To have a quality home built, you will pay @$120 per sq. foot minimum.  A MH cost considerably less than that
4.  We are not planning on selling the home, so who cares if it depreciates?
5.  Thanks to this economy, our age, etc., we are not willing to spend everything we have to have a roof over our head.  We want something we can afford in our old age
6.  My company offers a 7 year warranty on our homes.  I do not know of any site built homebuilder that will offer a 7 year warranty.
If you are not planning on selling your home for a long time, a manufactured home may be a good option.  The financing for a manufactured home is easier to obtain these days than stick built homes.  If you like the freedom of living in your own home with some land, in this economy, a MH may be a good investment.  You can always rent it out later.  Manufactured Home dealers have finance companies they deal with.  People that are turned down for stick built homes b/c of their credit, etc. come to us and we put them in homes every single day.
Now for modulars.  Modular homes are built according to an IRC code (International Residential Code).  They have more lumber and they are placed on a concrete slab.  The home is built in modules and then transported and placed on the slab.  The only reason you would want to buy a Modular Home is if you want to put it in a neighborhood or subdivision with other site built homes.  When reselling a Modular home, it must be compared with other site built homes because it is a site built home.  Modular homes do hold their value better than Manufactured Homes.
I am a salesperson for a manufactured/modular home builder.  That is why I know about them and how they are constructed.  There are some Manufactured Homes that I wouldn't touch with a 10 foot pole because I know the manufacturer.  Like I said, we are purchasing one from my company so I must feel comfortable with it.  You can get some beautiful homes with tape and texture, etc.  The important thing is how they are constructed and the materials used - not the cosmetics.  With regards to hurricanes and tornadoes, many site built homes cannot withstand the winds of those storms.   Our homes are built according to Wind Zone standards.  In Texas, 95% of homes are built for Wind Zone I, which states that the home must be able to withstand winds of 120 mph.  If greater than 120 mph winds are frequent where you live, you can have the home built to a Wind Zone II or III.
I have a blog on this very subject, if any of you are interested, pm me and I'll give you the link.  My latest blog has to do with what to ask a Manufactured Home builder when shopping for a Manufactured Home and what to look for.