I'm lucky and have had pretty good experiences with DMs across the board... though I began DMing at an early age and never really looked back.
Here are three (relatively mild) stories.
~There's a DM who's tried to rope me into her ongoing 1E campaign a few times... I always end up sidling away after a session or two, because her world is so rife with important NPCs (who are as or more important than the party) that most game sessions devolve into her talking to herself.
~One time a DM who is in general excellent (but can occasionally get bogged down with pacing) offered to run a quickie one-shot for a few hours one night. He spent 3 of the four hours IC roleplaying with one of the PCs, trying to convince her that she wanted to go on this expedition. The rest of us sat around fidgeting, wondering how long it would take for him to say "OK, if you don't want to come, don't come." It took 3 freaking hours. We never even finished the first combat.
~My other bad experience has been during a PbP. It was a PbP I joined over on GitP while the old boards were down, and I was jonesin'. This was the DM's first time behind the screen after alleged years as a player. He requested tier 2-4, so I decided to run with a Wizard/Druid/Arcane Heirophant, going for a kind of party buffer + SuperFamiliar build, as something fun and not overpowered. He approved my choice; he said no early entry into AH, but that wasn't too big a deal.
The problem was when we started out on our first mission. He had originally said in his chargen guidelines that all WotC sources were allowed; when we discovered we were heading to a desert, I mentioned casually in the OOC thread that I would go pillage Sandstorm for some druid spells to help out. "No," he replied, "you can't use that book." Why not? "Because you can't get any spells from non-core sources that will help you deal with the environment."
Then, a little ways in, he told me that I couldn't have unlimited spells in my spellbook, since "a wizard can know every spell and that makes him overpowered." I'd be limited to twice the number of daily spell slots I'd have. Also, I wouldn't get any spells automatically from leveling, I'd have to report back to my mentor at the guild to add any spells to my spellbook. Which meant that if I leveled up on the mission and took my 3rd level of wizard, I was SOL for 2nd-level spells.
At that point, I was debating whether or not to leave the game. If you're going to nerf full casters, fine -- but don't approve a build and then nerf it after the fact. As it turned out, Skyrim came out and the DM disappeared, so the game died. I never had to choose to leave.