I have two and I've never had a problem washing in the machine. I put them in alone (they're both black), gentle, and I use Woolite for darks.
My mother usually puts hers in the machine, too, only with her last one, somehow the machine chewed up the handle. She was able to sew it back into place, though.
And if it has one of those fabric-wrapped cardboard bottoms, take that out! Mum left hers in by mistake once and ended up with shredded cardboard all over everything.