I took Sassy to Petsmart to be groomed for the first time last night! (I know, but read on...I had a great experience.) She's five months today; a lot of groomers require your puppy to have its rabies shot before you bring them in, so I'd definitely say after that. I personally wasn't comfortable taking her for awhile, so I had to work myself up to it.
I watched for awhile outside the window and saw a woman grooming a Yorkie & thought she did a great job, so I went in and made an appointment with her personally.
(See this thread for pics:
http://www.yorkietalk.com/forums/showthread.php?t=84369)
Petsmart will do a special puppy package up until they're five months old, and it was pretty inexpensive. I had her face, feet, and tail trimmed, and I also had her nails clipped. She looks great! I didn't want any length taken off of her yet, but I'm sure I will eventually. I didn't think I'd be comfortable taking her to Petsmart, but the staff were all really nice, and the girl who groomed her was super sweet to Sassy, so I'll definitely go back.