Its ok to wear lace ups, but Id be sure to find some closed laced one's. But its true, a formal slip on is more formal than lace ups.
.I've already posted an article about it and a further reference a couple posts above.
But, personal preference is personal..so feel free to tie it up!
Im just one of those people who have to correct a misconception no matter what it is...
edit: For those who dont want to read the article...
"You do not have to go the expensive route with shoes. However, the adage you get what you pay for tends to be clearly demonstrated when it comes to this area of your outfit. The best bet is to have a good quality pair of shoes that are darker in color than your suit. Black would be appropriate for any of the suit colors previously mentioned. When it comes to the style of your shoes,
there is not an appreciable difference between slip on loafers and lace up shoes.
Loafers are technically more formal, however, its easy for snow and slush to spill over the edge of loafers and leave you with the unpleasant feeling of wet socks. Keep this in mind if you are interviewing in regions where snow may be an issue"
"One of the first laws of fashion is that nothing undermines the effect of a perfectly good suit more unequivocally then a pair of fancy lace-ups..."
- Referenced Book: Handbook of Style by Esquire
Obviously not a big deal, but I do like being right...lol