I saw some slurs that span two staves (both the bass and the treble clefs) on a piece of sheet music. Are they any different from the regular slurs? How should I play them?
They might indicate voice leading: a phrase may begin in the treble clef and conclude in the bass clef, sometimes requiring you to "pass" it from the right to the left hand. The slur indicates this unity and that you should play it in legato.
Example: Haydn's keyboard sonata in G minor, Hoboken XVI:44 (mm 13-15) http://imslp.org/wiki/Piano_Sonata_No.32_Hob.XVI:44,_G_minor_(Haydn,_Joseph)