I wear the Focus Day & Nights. Sooooo nice. You only need to change them once a month, but I've been wearing mine for like, 3 months at a time for the past few years. Only problems I ever get are when Im tired and my eyes dry out or when I do stuff that makes my eyes all red and fuzzy...
I used to work in a warehouse that was really dusty and that caused some problems too occasionally. Hurts like a son of a bitch if you get some dust under a lens.
Keep a spare bottle of solution and an extra lens case at work for youself just incase your contacts ever irritate you really bad. It sucks having to suffer through a day of irritating contacts or having to just throw them away because you can't stand having them in at the moment.