I'm a huge fan of Flickr.
It's been a few years (maybe 4) since I've used photobucket, but, from my experiences it was very unreliable. I'd often get errors and my bandwidth would run out too fast and my pictures would end up being blocked. At the time I was using it the website was FULL of ads and I remember the layout being very not-so-aesthetically pleasing. I'd imagine things have changed since then.
I was introduced to Flickr by a photographer friend. My first impression was that everything was clean and easy to navigate. While I still had upload limitations my pictures never turned into the "excessive bandwidth usage" image. I found Flickr to be very community oriented with a wide range of users. From point-and-shooters to professional photographers. I've since upgraded to a pro account ($24.95/year).
Flickr does a great job of resizing your photos. I remember photobucket would really change the quality of the images I would upload. Flickr keeps your pictures as clean as they are originally.
In Flickr, choosing the "medium" size is the perfect height and width for posting pictures on the knittinghelp.com forums (the longest edge will be 500 pixels).
It's easy to print out pictures through Flickr (I just had a bunch of mine printed and they turned out awesome). There are other options as well, you can easily make calendars, posters, or books of your pictures (I've already made 3 books! Imagine a whole book of your FO's!). You can even turn them into postage stamps.
There are great systems for tagging and organizing your photos and there are four levels of viewing 'privacy'. Flickr allows other members to comment on your photos as well as letting you see how "popular" your picture is based on how many views your image gets, how many comments, how many people add your image as a favorite... there's also an interesting-ness formula... not too sure how it works but it's cool.
Can you tell how much I love flickr? =)
There's a nifty little tool called 'notes'. It lets you put ... well, notes on your image. Instead of adding a caption that says "Malabrigo. From left to right: solymar, pink frost, velvet grapes" You can actually put little 'invisible' boxes on your image.. so people can just mouse-over a certain cake of yarn and a little text block will pop up and say "amber gold"... I think this might only work with other flickr users, though.
I think that's enough for now! If anyone wants more reasons to use flickr just send me a message.