I had loads on mine recently. Clayed it for the 1st time and was sooo pleased with the results. Takes quite along time to do it properly, but well worth it.
I clayed my car last summer. But since then I have just used AutoSmart Tardis (as mentioned above). Its fantastic so I would recommend this to anyone rather than claying.
My car was covered in tar in January, took me ages getting it back all sparkly lol. All the snow, grit and winter sludge