I'm not aware of any Windows software that offers the same tagging capability as what's available for the Mac. Mainly because most of the grunt work is handled by the OS indexing. However, I'm still using XP so perhaps someone on the forum has some information with regards to Win 7.
Hmmm, bloat. As you said, I think it can be a problem with any PIM tool you use with any frequency. At least that's my experience with them. I'm mainly a visual person, and while PBs search capability does have room for improvement, i found the visual linking more than makes up for it. To cope with a large database I use a combination of:
Context sensitive naming (the comma trick). I find if I use it for related sub-topics it's invaluable for quickly finding information in quicksearch. I don't always keep the grandparent or parent name, just whichever term I'd search for most.
Tags and types. I started implementing a category type when my brain got over a certain size. I also started assigning colors to my types, supertypes and tags so I can easily distinguish them in quicksearch or reports. I also use a "currently" and "frequent" tag combined with "work" and "home".
Reporting. With the new report filtering capabilities in 5.5 I've been using reports much more now. With creative tagging and types, you can use inverse filters and target sections of your brain.
On the attachment side of things I have three categories, work only files, home only files, and files I need at both places. I'm a huge fan of Dropbox, it has singlehandedly made using one database at work and home not only possible, but easy.
Over the past five months or so, I moved all of my work only files out of PB and into one folder. This makes things very simple as if I move to another machine, I just have to put that folder in the same location, and all my shortcuts are still valid. It makes backing things up easy also. Finally it reduces Brainzip size, and the Dropbox space requirements.
Several things Ive learned. When you copy a shortcut attachment in PB, it copies a shortcut, not the actual file. This can be a bit annoying. When I need to copy the actual file I either open the containg file and use best-fit typing to find, or right-click and send by email. This attaches a copy of the actual file, not the shortcut to the email and you can then drag it out of the email and place wherever.
My usage for files I only use at home is generally cleaner as I use a combination of Leap and PB, depending on what I'm doing.
Files I need at work and home I add as PB internal attachments. Dropbox syncs them in both places, so they are readily available. Since these files are generally things I'm currently working on, they are usually tagged as "current" and I can decide to move the files out when I remove the tag.
This helps keep things lean as possible.
For searching I generally start with quicksearch, and with multiple word fragments to narrow the thought name returns quickly. If necessary I go to extended search. When I find the thought I sometimes adjust the thoughtname, add verbiage to the label or the notes as appropriate. I almost never need to access extended search.
Sorry about the great wall 'o text. I hope this at least gives you some further ideas or direction.
Java SE 6