In conjuction with the owner of the MacBook, we decided not to stick the new battery down, specially because it is used 99% of the time on a stand and connected to a monitor. Will repost if this seems to give any issue.
In fact I think each of the three speaker screws are of a different length.
With the help of some acetone a little syringe and a credit card, I found the whole battery removal part to be easier than I expected.
Like Peter, I just folded it back a bit and had care to keep it out of the way. I think it is much better than the risk involved with taking it out.
All in all it found it a bit less difficult than I expected - As with all the work I have done on different Apple products: Slow and careful work and following the instructions - including all the comments - seems to be the best advice.
I have a late 2009 27" Mac and did something similar to Gabe, but being alone, after unplugging the vertical sync cable, I used two wooden chopsticks to hold the screen at about 45° and without disconnecting any more cables I could quite easily access the Superdrive to remove and replace with a 240GB SSD with help from a caddy from TheNatural2020, which required a tiny modification.
All in all it took me about 45 minutes and was much easier than expected. It is working at a negotiated SATA speed of 3 Gbps Some report a speed of only 1.5 Gbps, but from what I had read before purchasing the Crucial M500, going for a 6 Gbps SSD is worse on a late 2009 Mac as it has to default to the basic SATA 1 speed of 1.5 Gbps, while the slower 3 Gbps SATA II drive works at 3 Gbps. The time from the Apple logo till the sign-in screen on startup has gone from 33.5 seconds to 8.5 secs, and my internal hard drive is a 7200rpm
I am VERY satisfied and it was much easier than expected.