There is nothing like that nice golden new teak look. BUT...it takes a lot of work to get it there and to maintain it. If you decide you want to restore, the process varies according to the condition of the teak. If the teak has no residue from varnish or other sealers AND the wood is fairly smooth you could get away with a cleaner (On and Off, or a good one part cleaner/brightener). However, if the grain is raised, which often happens when the teak is left to gray, you will need to sand smooth. Sanding may be enough, but often you will also need to use a cleaner/brightener, or even the more agressive two part cleaner/brightener (read labels) then lightly sand again before applying whatever sealer you opt to use. No matter what you do, it will need to be re-done every few years - hence the argument for leaving it gray.