Get a transfer switch. It's worth the extra money. That's what I did. I have an 8.5k generator hooked up to a 30 amp, 10 circuit, transfer switch. I have my water pump, oil boiler, bathroom, 2 bedrooms, living room, kitchen, freezer, and 1 downstairs light hooked up.
Total cost w/ generator and hook-up was $1,200. My coal boiler will be hooked up with the oil boiler on the same circuit. My electrician said that this will be fine.
Having standby power is great, especially where I live. The winters are very long and cold. Just this past winter the whole town was out of power for nearly 3 hours. I placed a call to the power company and was told that it could be out for 24-48 hours.
It was quite cold out. I stepped out into the garage, wheeled the generator out back, hooked up the cord, and then started it. I went back indoors, moved 1 switch and VIOLA!!!
One of my friends drove by and called me on his cell phone. He asked if we were the only ones who paid their electric bill!!
It's very hard to put a price on piece of mind.