As a side project I built TwitterAudit (which is under a lot of load right now and runs on a 512mb VPS :) to estimate how many followers are real vs how many are fake. It looks at a sample of 5000 followers and about 5 criteria to guess whether a given user is real or fake... check it out!

Labmeeting.com is a relatively new site (compared to Citeulike) for life-science researchers. You can upload all your PDFs and it will automatically determine the associated Pubmed records. You can add papers to multiple folders and it supports fulltext searching (assuming you have uploaded a PDF). It is free for academic users.

You can also read your PDFs from anywhere (through Scribd, embedded into the site).

Check out a sample paper page

You can also import/export citations from/to a bunch of formats (BibTex/RIS/Endnote).

There are a whole bunch of other interesting features on Labmeeting that I didn't mention here, so just check it out.