As companies like Google (GOOG) and Facebook (FB) continue to eye the mobile market as they look to bolster their advertising portfolios, a new report suggests mobile might not be the golden goose some had hoped. An estimated 61% of cell phone owners in the United Kingdom use smartphones, and a whopping 53% of them say they have never seen a mobile advertisement on their handsets, according to a recent Nielsen study. Econsultancy notes that mobile advertising grew 132% in the first half last year. With more than half of smartphone users in the UK claiming to have never seen an ad, the next push in mobile advertising will likely focus on finding ways to display mobile ads more prominently.