It may be common but the more important question the investor will have is how soon and for how much you can sell the company (in other words how will you use the funds to create more value / reduce risk in the startup). There will be other terms associated with a funding that will have a significant impact on how much you make when you sell (for a reasonable range of exits). A couple of good sites for background on funding:
http://venturehacks.com/
http://www.feld.com/blog/archives/cat_term_sheet.html
http://www.startupcompanylawyer.com/?s=term+sheet
http://www.paulgraham.com/guidetoinvestors.html
http://www.skmurphy.com/blog/2007/12/01/three-points-about-s...