Ill have to get it in my hands, because thats the determining factor for me. We can pixel peep all we want but once we buy it we are stuck toting it around for 100s of hours so imho ( even though im new ) how it feels in your hand and how comfortable you are with it should be at the top of the list.
However as someone who started on an a300 and has recently moved to an a700, I can say for me personally Live View ended up being used almost every outing. Then again im huge and dont feel like plopping down on my belly nor climbing. If I get a 550 in my hands and it has a reasonable viewfinder then I got to think that its balance of features is sweet. Luckily for me my wife has joined into this hobby with me and she will need a upgrade to her a350
I would not give up my new a700 for the LV and viewfinder on the 300/350 again ( its almost painful to look through now ) however if they have pulled off a good compromise i will definitely consider it. I got to say 7fps, lower noise sensor ( my buddies 40d blows my a700 out the water in the 1600 and up ISO noise department and I am using a much better lens ), HDR, 3" 920k, 2 lv modes, at $50 cheaper than i just paid for my 700. Yea i got to look at that.
The build of the 300/350 was ok with me and its my understanding that the 550 is much more similar to them than the 330/380 which i hated in the store. I can feel my a700 is a higher quality machine no doubt but it really doesnt matter much to me. Im new so i dont have any preconceived notions about systems and/or the inclinations of equipment snobs. Being a new guy I just want to put the best camera i can put in my hands to produce the best photos possible at the cheapest price......
Newbie or not i think its hard to argue with the Sony system and price/performance how does one get better than a 14mp Cmos processor at 7fps with a 3" 920k screen for under $1000 with in body stabilization.
I almost pulled the trigger on a move to the 50d when i purchased my 700 but a quick total of what it would cost me to replace my current lenses and have them in IS quickly deterred me from that....