I have worn a sew-in for 3 months once, and I had no problems taking it out. Plus, I would wash the hair once a week. It was easy to take down and easy to remove shed hairs.
I first tried my first sew back in 2009 and I kept that in for 2 months. My stylist washed it once a week, and flat ironed the section of hair that was left out. I didn't know any better, and that section ended up with heat damage. It was a straight weave style (like I said, I didn't even know that I could have gotten a full sew in if I wanted it straight)
The second time around (which lasted for 3 months - January 2010) netted me good growth. It was actually 1.5 inches, but it seemed like a lot after having not seen my hair for so long. The one downside was that my stylist had braided too tight, then the weave was too tight, and the end result was a section in the crown that had broken off to about an inch
I never got it re-tightened though, I think the weekly washing hurt me because I was massaging pretty thoroughly in the crown area. The hair was Halley's Curls and I wanted to maintain the curly look.
If I get a sew in, I am going to do it myself now that I can properly cornrow.