I hate long songs. I get bored. If you asked any of my friends they'd tell you that i reach maybe halfway through songs that're 8+ minutes long, then skip them.
The only time I can tolerate "long songs" is if it's in the style of Enter Shikari's album Take To The Skies. The album, when listened to in order, sounds like it's one big song, but it still does sound like seperate songs, because they vary wildly from each other but still fit together in a seamless way...
Edit: Longest song I like is Borgore - Gorestep's Most Hated. It's 43 minutes long... It's still technically one song but it's similar to Enter Shikari's album in that the different parts are very distinctly different.