Hmmm, I have been sooo many times that it is hard to remember the gaps. But, I think my longest gap was 4 years. When I first met my hubby, I took him to Epcot for his birthday. He made it clear at the time that theme parks aren't his thing and so I didn't return for at least 4 years. Then, after we were married, it finally hit me. So what if you don't like Disney? I do! So, we started going again with my first return to The World being for Xmas 2004 I think.
Since that trip (which was a disaster) we've returned on July the 4th, 2005, October 2005, December 2005 (2 trips), April 2006, May 2006, June 2006 (with a second trip in June coming up this weekend), trip planned for July 2006 (for oldest son's brithday), trip planned for September 2006 (for business), trip planned for late October 2006 (for youngest son's birthday), and I'm sure we'll go around the holidays too.
Of course, we only live 4 hours away so it's much easier for us to go back often, especially with an annual pass but I still envy those that live only minutes away. If only ....