There are at least two kinds of autobiographies: the ghost-written, orange-tanned "Heat" celebrities who are famous for being famous and then there is the Sir Ranulph Fiennes type , who have a lifetime of honourable achievement to look back and reflect upon. While not at the level of the former, Simon Pegg's Nerd Do Well certainly isn't in the latter camp either.
It takes a special kind of conceitedness to have written an autobiography by the time you are forty (albeit not achieving Kenneth Branagh-levels of self-satisfaction). Perhaps Simon Pegg is marking the end of a significant chapter of his life and the beginning of a new one. Regardless, Nerd Do Well is a lightweight but entertaining, nostalgic journey of fairly average abilities of self-discovery, couched in an ironic, self-effacing manner.
The first two thirds of this book are mostly entertaining, concerning as they do a young lad's formative experiences growing up in a small English country town and the whole rites-de-passage thing (or right of passage, as the French would say). The final third is essentially the same celebrity anecdote repeated with variations: "And then I met [famous name] - if only my younger self could see me now, he would probably soil himself!" So we get to hear about Pegg visiting the mall where Dawn of the Dead was filmed, meeting actors from Star Wars and that kind of thing.
Intercutting all this is a funny piece of deliberately bad science fiction in which Pegg the rugged action hero (along with his faithful gold robotic butler, Canterbury, who is nothing at all like CP30), foils the overly elaborate plot of some fiendish criminal mastermind.
It seems that some readers are unhappy that there is not much information about the making of Spaced et al but I would suggest that the dvds have more than enough material covering this facet of Pegg's life.
That said, if you enjoy Simon Pegg's authorial voice, you'll find a lot that tickles you in his modest autobiography. Witty and diverting, Nerd Do Well is a quick and easy read, in the same vein as Peter Kay's The Sound of Laughter.