I abandon the registration process in about 30% of places that choose to register to try a service – and I rarely get interested enough to register, all because I can not use a perfectly valid email address containing a plus sign. Other 40% does the correct validation, in the remaining cases, with discomfort, I register without using an email alias without the plus sign.
C’mon people your are loosing a possible clients because of incorrect, to tight and irrelevant email validation. You send the confirmation email any way, right? You shouldn’t care what email I provide, if it gets delivered you get your confirmation and a client. If you need to validate the email address during registration at least do it properly!