The IRS just sent out an email that indicates that 70% of taxpayers used efile last year.
There are a lot of reasons to use efile.
1. you don't have to mail to the IRS, no postage, no wasted paper (think green)
2. as there is a accuracy check on all efiles, the odds of a paper audit are greatly reduced.
3. you get your refund at least a week faster.. if you use direct deposit, you refund should get to you in 8-14 days. The way they work it is if your return is received by Thursday morning, the refund will be deposited the following Friday.
If you don't use DD, then the refund is delayed a week longer, plus maililng time.
Mailed in returns have to allow for 4-6 weeks to get a refund.
4. If you owe, if you eflile you are guaranteed that the IRS rec'd your return. If you mail it and it somehow gets lost, then you would be subject to late filing penalties .. which are 5% per month up to five months.