Yes, it is littering. It looks ugly and messy.
At least one municipality defines it thusly:
Littering Fees and Charges
Littering Infringement Fees 2008/2009
Minor Littering
Infringement fee $100
Minor littering is defined as depositing in or on a public place or in or on private land without the consent of the occupier: Cigarette butts; Wrappers/paper; Chewing gum; Small food waste; Take-away food/drink containers; Fish & chip papers; Plastic drink bottle(s); and Aluminium can(s).
NB: For cigarette butt littering, this is a two step enforcement process.
First step: Educate/warning – offender advised this is not acceptable.
Second step: If a person is found depositing cigarette butt litter having already been warned, an infringement fee of $100 will be issued.”
http://www.huttcity.govt.nz/Council-Services/Fees-and-Charges/Littering/
The entire state of Georgia has considered discarding cigarette butts to be littering and has done so for the past 22 years ( http://www.legis.state.ga.us/legis/1997_98/leg/fulltext/hb248.htm )
And then there is this:
Cigarette filters are 100 percent non-biodegradable and made up of a plastic compound called cellulose acetate, which contains toxic chemicals
These toxic chemicals can seep out and pollute everything it surrounds
It can take a single cigarette more than 15 years to disintegrate naturally
1 single cigarette butt can pollute 40 l of drinking water
(http://www.squidoo.com/helpnature#module8978508)