TS,
I shoot on average about 100-200 digital photos a week (lots of little nieces and nephews growing up way too fast). What I typically do is upload the JPG images (the ones that turn out OK

) to Costco online, then pick up the prints at the local warehouse. Size 4x6, single copy. The ones of which I want extra copies, or enlargements, I print myself at home. I shoot RAW and JPG simultaneously, so the ones I print myself I first post-process the RAW file in Nikon Capture and Photoshop.
I've owned various Epsons and H-P's in the past, but the printer I currently use is the
Canon i9900, and it is the heat (can I use that term for a non-tactical product???) It's been awhile since I've checked the reviews, but when I bought it about a year ago, this printer was consistently ranked first or second by various reviewers. It can print up to 13x19 prints. I print 8x10's regularly, and they come out great. One of the things I like best about it is, with 6,144 nozzles, it prints
fast.
As to your second question, if you are only printing a couple hundred prints a year, I would send them out, even for enlargements. As x_ and Kyo detailed, supplies go fast. For example, the Canon i9900 has 8 ink tanks. Start printing out a bunch of 8x10's and those suckers drain fast. Not to mention the time involved. If I don't care about cropping, sharpening, color touch up, etc., I would rather send the pics out.
My own bias is that if you are going through the time and expense of printing at home, you should be shooting RAW. Although digital cameras these days are very good, a JPG straight out of a camera will never beat a post-processed RAW in image quality.