You can get along without a transfer switch as long as
you never make a mistake, but it only takes one mistake
to cause you to wish you had installed one.

I ran a home gen for several years without a transfer
switch - I had the gen cord (with male plug) wired into a
spare two-pole breaker and an air-conditioner type
disconnect in the garage in line with the cord so that the
possibility of a 'suicide cable' configuration was
diminished. I knew what to throw/connect/disconnect when
and everything worked fine... I was confident with my
knowledge and ability.

Well, during one power outage I did something in the
wrong sequence and all it did was trip the breaker on
my generator, but it scared me *big time*. I immediately
bought a new one of these
(http://www.connecticut-electric.com/10-12K1.asp) on eBay
for about half of the store price, selected the circuits
to use with it and installed it properly. Now, even my
wife can get the backup power going (well, almost): She
fried the garage door opener and several other items by
not having the twist-lock plug shoved in completely into
the generator - it was thus connected without a neutral
and several items in my house took offense to this
configuration.