I've always done mine myself - that way I know what's been done and there's only me to blame.
I, however, am a mechanical idiot with no facilities bar a roof over Henrietta's head, so am content for Williams to look after her. Whilst I would rather not pay £400 a time, I can remember my Suzuki Swift 1.6 saloon (the most beautiful meatallic red I have ever seen

) cost me £325 or so a time to service in 1990-92 and that was every
6
000 miles - which took 8 weeks to rack up back in those days

.
I remain in awe of you guys who know what your doing!
Cheers
Jeremy