Hi - I was just there. I waited outside to go through security for about 20-30 minutes. Once you're inside they give you a number, and I stupidly just sat down waiting for my number without reading the instructions on the number slip...you're supposed to queue immediately at one of the booths to check in and hand them your paperwork.
So, I waited almost an hour before they called me up. After that it was about another hour - really not that bad - I'm not sure how much extra time I added on though! Plenty of room to sit though, and you can take your phone in now so that was nice. They complimented me on all my paperwork being in order, sounds like missing forms, etc. can delay things - so just make sure it's all filled out!
If anyone else is wondering about the notary thing - I emailed the embassy and they said an address stamp could be used instead of a notary seal. So, the solicitor at my husband's company signed it and put their company address stamp where the notary seal would go. No problems at all - they didn't ask me anything about it, even though I had their email and all sorts of back up evidence ready. They didn't ask for my transcripts or anything either.
I was really nervous about the whole thing - used to dealing with the awful DMV in my hometown in the US, so I was convinced I'd be wasting a trip to London having missed some obscure requirement - but in fact they were very nice and all was fine.
One thing - I brought my mom with me, but didn't realize you have to book an appointment for anyone accompanying you. I didn't go back to check the website - don't know where this info is provided, but just a heads up for anyone. In the end, it was better for her as she didn't have to wait the two boring hours
Also, I wore my baby in a wrap and that worked out well.
Good Luck!