I've got a Rockshox Recon fork on my mountain bike, so a tiny bit up from the more budget offerings. SRAM recommend 50 hour and 200 hour services. I don't keep a terribly accurate record of when I've serviced it so I just go off of feel really. I've owned the bike two years now and have performed a few 50 hour services. It's really simple to do and doesn't take too long so it's a bit of a no brainer really.
Early this year I also looked into the 200 hour service, it's a complete strip down and clean. There's no bike shops locally who will do it and I didn't want the hassle and expense of sending it away. So using the excellent SRAM tech docs I just had a go myself. It went really well and it was surprising the colour of the oil that came out. It was also great to learn how the forks work. So I'll definitely be doing them again, possibly next February when I suspect I'll have done about 200 hours more riding since last time.
I definitely find the forks feel much better for a service and given it's fairly simple, especially the 50 hour one, I don't see a reason not to do it.