If you put a 1.4 and a 1.5 NOOK side-by-side, you'll see
noticeably slower page turns in My Library and in the various places like book details (the screens with the dots across the bottom). These screens aren't as critical as the Reading window, but it's interesting that page turns there are significantly slower when page turns in the Reading window are significantly faster.
If you put a 1.4 and a 1.5 NOOK side-by-side, the background of the Reading window is a bit darker on the 1.5 than on the 1.4. The background of the other windows is the same, and (therefore) lighter than the background of the Reading window. I suspect that the faster page turns in the Reading window are related to not displaying the background as "full white", and that the bolder fonts might have been done as compensation for the darker background. The bolder fonts are welcome in any event. Here's a photo that someone made of 1.4 and 1.5, showing both the darker background and the bolder type:
The Wi-Fi connection problems are mainly for people who just got their NOOKs. Since 1.3 came out, a number of people have been totally unable to get their NOOKs to work with their home Wi-Fi systems, either due to security system incompatibilities or in some cases due to router incompatibilities. A few people have reported that their NOOKs quit working with their home Wi-Fi after the 1.5 update. It's not clear if this really is further deterioration or not, but clearly the Wi-Fi compatibility problems that B&N introduced in the 1.3 update have not been fixed.
The sideloaded books issue occurs for B&N e-books that are downloaded to a PC using the Download button on the B&N site (not via NOOK for PC, for example), then sideloaded into My Documents on NOOK. NOOK 1.5 refuses to open them, while 1.4 opens them just fine. Some people without wireless connectivity have a number of those sideloaded B&N e-books, and were using them just fine prior to the 1.5 update. It appears to be related to B&N's naming scheme for e-books downloaded this way. The file names are ISBN-epub.v9.epub where ISBN is the EAN-13 number and the 9 apparently is a version number. Removing the "." ahead of the "v" reportedly makes 1.5 happy.