I may be one of the only people who didn't send a STD... we didn't use a TA to book our wedding (and its a smaller wedding - 25 people). We had a free hold on our very small hotel's rooms for 2 weeks, so I just sent everyone I was inviting an email with a link to our website where we had all of the information. I think I also laid out some details in the email for making a deposit on the hotel. A few phone calls, many emails, and 2 weeks later, almost everyone was booked! We had a few stragglers, but luckily the rooms were still free. We're sending invites (message in a bottle DIY) 2 months before the wedding as a formality and reminder to pay the balance on hotel rooms.