Having been in the software business for nearly 20 years I can state that from my own experiences, recruiters are overwhelmingly bad.
The thing is that there are big incentives for the recruiters. Where I live (Dublin) the recruiters finders fee would be around 30% of the candidates salary. In IT that could be a fair whack of money. That sort of incentive can cause some peoples morals to loosen a bit.
Here are some of my experiences...
Recruiters editing my CV to make me look more skilled or possessing skills I don't have.
Editing my CV so that it contains the right information, but the formatting has been destroyed and it looks terrible.
Costing me a job opportunity when I applied direct to a company and because I was on a recruiters system they demanded a fee when they learned I was made an offer. Because the recruiter threatened legal action, the company withdrew the offer.
Calling at me at work. Even on occasions calling me via the company switchboard.
Arranging interviews without my consent.
A recruiter shouting at me for cancelling an interview because I was running a 39 degree fever.
Taking my LinkedIn profile data and creating profiles on their own systems. I added a fake job to my profile to weed those ones out.
Individual recruiters taking my data from one company to the next when they themselves changed employers.
Refusing to delete my data from their systems forcing me to go to the Data Protection Commissioner.
When I went self-employed they started calling me asking if I would hire one of their candidates. Even though I said I was a one man operation and would stay that way - they kept calling.
One recruiter calling my wife when I blocked their number.
Of course different peoples experiences may vary, but in my case I can honestly say I have never had a good experience with an IT recruiter.