About 120 of the buses at the depot I work out of are fuelled by CNG, and will be progressively replaced in the next 2-5yrs (by Volvos - diesels presently but that could change). They're lean-burn, so need a lot of upkeep with the ignition to stay running nicely. The turbos in these Mercedes-Benz vehicles are also negatively affected by the dryness and lack of lubricity in CNG fuel; the wastegates frequently stick or burn up - so they need reconditioned turbos every 1-2yrs. When the turbo goes on one of these, walking would be quicker, even on the flat.
Personally I think CNG or LPG (Propane) are good fuels. In Australia of strategic significance given most of our fuel supply is refined off-shore and we only have about 3wks in reserve if the sh*t hit the fan.
Additionally, the industry simply didn't work hard enough to dispel the old wive's tales about fuel consumption, performance loss, etc and so they've kinda missed the boat. They have a chance with hybrids, if they get their act together.
Electric is promising, but I don't think it is the be-all and end-all of technology right now, contrary to what a certain egotistical blow-hard might have us believe (he's only talking it up because he stands to benefit from the downfall of "Big Oil").