Unfortunately the answer is Yes it can. Any other advice you receive will probably be based on peoples own experience. (see mine below)
I personally downloaded OCLF from the market by RyanZA, followed the instructions and my phone ran perfect with no LAG.
There are several different ways to LAG fix your Galaxy, however, they all basically do the same thing and as stated there is always a risk that if something goes wrong, then you won't be technical enough to fix it.
Sorry, but probably not the answer you were looking for.
You take a real risk when you lagfix or root your phone. I would suggest you read up on first hand experiences like those at the XDA Developer forum to find out how others have fared and how they've gone about it.
The method described by micstewart is the same one as I used and I've had no problems that I haven't been able to work out eventually.
I don't think its that common, and its almost always caused by a user problem (not reading/following the instructions carefully enough, not checking that 3-button recovery is available on their phone prior to doing any modding etc).